IS. DEPARTMENT QF AGRICULTURE, OFFICE OF EXPERIMENT STATIONS BULLETIN NO. 126. A. C. TRUE, Di STUDIES OX THE DIGESTIBILITY AM) NUTRITIVE VALUE OF BREAD THE UNIVERSITY OF MINNESOTA IX . D^CU V M?NT^iS»T. .13 o< U.S. DEPOSITORY OO-10O2. HARRY SNYDER, B. S., Professor of Chemistry, College qf Agriculture, University 0/ Minnesota, ami Chemist, Agricultural Experiment Station. WASHINGTON: GOVERN M E XT PRINTING OFFICE 1 9 3 . LIST OF PUBLICATIONS OF THE OFFICE OF EXPERIMENT STATIONS ON THE FOOD AND NUTRITION OF MAN. \<>i e.— For those publications to which a price is affixed application should be made to the Super- intendent <>f i ocuments, Union Balding, Washington, l>. <'., the officer designated by law to sell . Atwater. i Four charts, 20 by 4U inches.) Price per set, unmounted, 75 cents. *Bul. 21. Methods and Results of investigations on the Chemistry and Economy of Food. ByW.O. Atwater. Pp.222. Price, 15 cents. Bui. 2-s. i Revised edition, i The Chemical Composition of American Food Materials. ByW.O, Atwater and A. P. Bryant. Pp. ST. Price, 5 cents. Bui. 29. Dietary Studies at the University of Tennessee in 1895. By C. E. Wait, with comments by W. O. Atwater and C. I>. Woods. Pp. 45. Price. f> cents. Bid. 31. Dietary Studies at the University of Missouri in 1895, and Data Relating to Bread and Meat Consumption in Missouri. By II. B. Cibson, S.Calvert, and D.W.May, with comments by W.O. Atwater and C.D.Woods. Pp.24. Price. 5 cents. *Bul. 32. Dietary Studies at Purdue University, Lafayette, Ind., in 1895. By W. K. Stone, with com- ments by W;0. Atwater and C. D. Woods. Pp.28. Price, 5 cents. Bui. 35. Food and Nutrition Investigations in New Jersey in 1895 and 1896. By E. B. Voorhees. Pp. 4u. Price, 5 cents. Bid. 37. Dietary Studies at the Maine State College in 1895. By W. H.Jordan. Pp.57. Price, 5 cents. Bui. 38. 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S., Professor of Chemistry, College of Agriculture, Universit;/ of Minnesota, and Chemist, Agricultural Experiment Station. WASHINGTON: GOVERNMENT PRINTING OFFICE 1903. OFFICE OF EXPERIMENT STATIONS. A. C. True, Ph. D., Director. E. W. Allen, Ph. D., Assistant Director and Editor of Experiment Station Record. C. F. Langworthy, Ph. D., Editor and Expert on Foods and Animal Production. NUTRITION INVESTIGATIONS. W. 0. Atwater, Ph. D., Chief of Nutrition Investigations, Middletown, Conn. C. D. AVoods, B. S., Special Agent at Orono, Me. F. G. Benedict, Ph. D., Physiological Che mist, Middletown, ''arm. R. D. Milner, Ph. B., Editorial Assistant, Middletown, Conn. 2 LETTER OF TRANSMITTAL r. S. Department of Agriculture, Office of Experiment Stations, Washington,, D. C, Fdruary 15, 1903. Sir: I have the honor to transmit herewith, and to recommend for publication as a bulletin of this Office, a report of investigations on tin 4 digestibility and nutritive value of bread carried on at the Uni- versity of Minnesota in 1900-1902 by Harry Snyder, professor of chemistry in the State university and chemist of the agricultural experiment station. The studies were conducted under the imme- diate supervision of Prof. W. O. Atwater, chief of nutrition investi- gations, and Prof. Charles D. Woods, and form a part of the investi- gations on food of man conducted under the auspices of this Office. Thanks are due the Northwestern Consolidated Milling Company, of Minneapolis, Minn., for specially grinding samples of hard wheat, and to the Goshen Milling Company, of Goshen, Ind., and the Christian Breisch Milling Company, of North Lansing, Mich., for similar favors with respect to soft wheat. The results of these investigations are in accord with those obtained in former studies, and indicate that fine patent flours from both hard and soft wheat are more digestible than corresponding coarse flours, though they contain somewhat less protein and mineral matter pound for pound. The investigations also show that all flours are quite thoroughly digested, and furnish experimental proof of the generalh' recognized fact that wheat flours of all grades are among the most important articles of diet. Respectfully, A. C. True, Director. Hon. James Wilson. Secretary of Agriculture. 3 CONTENTS. Page. Introduction 7 Methods of Bampling and analysis 8 Description of samples of food materials 10 Composition of samples of food materials 12 Composition of feces and urine obtained in digestion experiments 17 Experimental methods 18 Details of the digestion experiments with bread from different grades of hard spring wheat flour 20 Digestion experiment No. 242 21 Digestion experiment No. 243 22 Digestion experiment No. 244 23 Digestion experiment No. 245 23 Digestion experiment No. 246 24 Digestion experiment No. 247 25 Digestion experiment No. 248 26 Digestion experiment No. 249 26 Digestion experiment No. 250 27 Summary of results obtained with hard spring wheat products 28 Details of the digestion experiments with bread from different grades of soft winter wheat flour 32 Digestion experiment No. 309 32 Digestion experiment No. 310 33 Digestion experiment No. 311 34 Digestion experiment No. 312 35 Digestion experiment No. 313 35 Digestion experiment No. 314 36 Digestion experiment No. 315 37 Digestion experiment No. 316 38 Digestion experiment No. 317 38 Digestion experiment No. 318 39 Digestion experiment No. 319 40 Digestion experiment No. 320 41 Digestion experiment No. 321 41 Digestion experiment No. 322 42 Digestion experiment No. 323 43 Summary of results obtained with soft winter wheat products. 44 General summary of results and conclusions 50 5 ILLUSTRATIONS. Page. Plate I. Fig. 1. — Flour particles from straight patent floor No. 240. Fig. 2. — Flour particles in >m entire-wheat rlour No. 241 4S II. P"ig. 1. — Flour particles from graham floor No. 24.;. Fig. 2. — 1 from bread fin mi straight patent rlour 48 III. Fig. 1. — Feces from bread made from graham flour. Fig. 2. — Ft- from bread made from entire-wheat rlour 48 6 STUDIES ON THE DIGESTIBILITY AND NUTRITIVE VALUE OF BREAD. INTRODUCTION. The investigations reported in this bulletin, which were carried on at the University of Minnesota in 1900-1902, are a continuation of the experiments on the digestibility and comparative nutritive value of bread made from different grades of flour reported in previous bulle- tins of this Office, and include two series of digestion and nitrogen metabolism experiments with healthy men on a diet of milk and bread made from different grades of wheat flour, namely, straight patent, entire wheat, and graham. In the first series, which included 9 experiments carried on in 1900-1901 (pp. 20-31), the different grades of flour used were all ground from the same lot of hard Scotch Fife spring wheat. In the second series, which included 15 experiments, carried on in 1901-2 (pp. 32-50), the flours were ground from soft winter wheat. The standard grades of flour produced by the modern process of milling are discussed in detail in a former bulletin 6 and also in later pages of this bulletin. Briefly stated, by graham flour is meant the product obtained by grinding the entire wheat kernel. Entire-wheat flour is the product obtained by removing about one-half of the coarse bran before grinding. This flour is liner than graham, but not as tine as the patent grades of flour. In milling the patent flour all of the bran is removed. Several grades of patent flour are produced, but the one most commonly found on the market, known as " standard patent,' 1 "straight patent," or "straight grade" consists of the first and second patent and first clear grades combined. By ordinary proc- esses of milling a little over 72 per cent of the total wheat is recovered as straight or standard patent flour and about 2.5 per cent as low grade and "red dog" flours, the remaining 2d percent being returned in the form of bran, shorts, and other offal. During late years the relative food value and merits of these differ- ent kinds of flour have been the subject of extensive discussion; but an examination of the literature on bread and flour shows that but few digestion experiments which are really directly comparable have been "V. S. Dept. Agr., Office of Experiment Stations Buls. 67 and 101. H\ S. Dept. Agr., Office of Experiment Stations Bui. 101, pp. 7,8. 8 math 4 with the different kinds of flour. Wheat ranges in protein con- tent from about 11 to IT per cent; therefore, in order that the results of experiments may be comparable, the three kinds of flour should be milled from the same lot of wheat. In the former report it was shown that when the three different kinds of flour were ground from the same lot of hard spring wheat the graham and entire-wheat flours contained a little more protein and gave a slightly higher fuel value than the straight patent flour; but the coarser graham and entire-wheat flours had a lower coefficient of digestibilit} r than the liner straight patent flour. Hence the straight patent flour furnished the body more nutritive material per gram or per pound than either the graham or entire-wheat flour. Because of the importance of the subject and the extensive use of wheat as a human food it was deemed desirable to repeat the w T ork, and in so doing to extend the periods of the digestion experiments over a longer time than in the case of the experiments previously reported, in which they were only two da\ T s each. The experiments of 1900-1901 were therefore practically a repetition of those of 1899-1900, except that the digestion period in each case was twice as long, i. e., four days. In 1901-2 experiments were made similar to those of 1900-1901, but with soft winter wheat, which is somewhat different in character from the hard spring wheat, in order to determine whether the results would be the same with flours ground from different sorts of wheat. In connection with both series of experiments a number of analyses were made of the varieties of wheat studied and of their milling products as well as of the milk which formed a part of the diet in the digestion experiments. The necessary analyses were also made of the feces and urine to secure data for use in computing the .digestibility of the food and the balance of income and outgo of nitrogen. METHODS OF SAMPLING AND ANALYSIS. The analytical methods employed in these investigations were prac- tically those recommended by the Association of Official Agricultural Chemists/' a few modifications suggested by experience being intro- duced. A sample of each loaf of bread used during the separate digestion experiments was analyzed. One hundred grams of bread was reserved for the dry matter determination, and proportional parts of the dry matter of the bread from various loaves were united to form a com- posite sample, which contained a part of each loaf of bread propor- tioned to the size and moisture content of the loaf. A composite sample was made of the milk in the experiments of 1900-1901 by saving, in a bottle containing 100 milligrams of potas- " l". S. Dept. Agr., Division of Chemistry Bui. 46, revised. shun bichromate, 25 cubic centimeters of the mills used ut each meal. In the experiments of L901 2 the amount of milk reserved at each meal was 50 cubic centimeters. The temperature of the drying oven was kept at about 60 C. in all cases of the determination of moisture in the feces. The bread was also dried at this temperature. Nitrogen was determined by the ordinary Kjeldahl process. In the case of wheat and its milling products and bread, protein was obtained by multiplying nitrogen by the factor 5.7. In the case of protein in the milk and the (vers the factor used was 6.25. No attempt was made to separate and determine the amount of metabolic nitrogen of the feces. Carefully purified ether was used for determining ether extract in the bread and feces. The results obtained for the fat in the U^-^s were not satisfactory in many cases, although the determinations were made in duplicate by the method generally followed and considered reliable. The fat in the milk was determined by the Adams gravi- metric method. The ash was determined by combustion at a low tem- perature. The carbohyd rates were estimated by subtracting the sum of the protein, ether extract, water, and ash from 100. The determination of the ether extract in the feces necessarily inyolyes an error, owing to the metabolic products present. Another source of error is in the protein determination. While the determi- nation of the total nitrogen is satisfactory, the factor for conyerting this nitrogen into protein is not perfectly reliable, and in many cases is very unsatisfactory. It is well known that not all of the nitrogen of a food is in the form of proteid compounds. In the case of the food materials used in these experiments, namely, bread and milk, over 97 per cent of the total nitrogen is in the form of proteids, and the error from nonproteid nitrogen in the food is therefore small. In the case of the feces, however, the kinds, proportions, and composi- tion of the nitrogenous ingredients are not well understood, and the estimate of " protein" is at best very crude. The errors involved in the determination of carbohydrates, by difference, are too well known to require discussion. Notwithstanding these imperfections of analyt- ical methods, which are not peculiar to these investigations but are common to all similar experiments, the results obtained in determining moisture, ash, total nitrogen, and heat of combustion are believed to be reasonably accurate, and the deductions drawn from them are regarded as reliable. The calorific value or heat of combustion of the various samples of food, feces, and urine was determined in the usual way by means of the bomb calorimeter. In the case of the milk and urine, weighed blocks of cellulose were employed to absorb the liquid. The absorp- tion block was saturated, carefully dried, weighed, and again satu- rated with a weighed quantity of material. After drying at a tem- perature of 65° C. the block was burned in the calorimeter in the 10 usual way, a correction being made in the results for the heat of com- bustion of the block employed. DESCRIPTION OF SAMPLES OF FOOD MATERIALS. In the milling of the hard spring wheat great care was taken to secure representative samples. A- in the former work, the milling whs carried on under the supervision of Mr. ('. E. Foster, of Minne- apolis, in one of the large flouring mills of that city. Two hundred pounds each of the three different kinds of Hour were obtained from the mill. As soon as the samples were received at the laboratory smaller samples were drawn for analysis. For the experiment- with -oft winter wheat difficulty was experi- enced in securing sample- of soft-wheat flours that were comparable with the grades of Hour used in former work with hard spring wheat. The samples of hard wheat used in 1899-1901 were exhaustively milled and very little flour was left in the bran and middlings. The samples of soft wheat used in 1 ( .*< )1— 2 were, as is the custom with such wheats, less exhaustively milled and more flour was left in the offals. For this work sets of samples were obtained from two differ- ent milling companies, and in each case the different grade- of flour were from a single lot of wheat. A description of the different sorts of wheat used in the experiments, and of the different grade- of flour and milling products made from them, is here given. These are the -amples the analyses of which are reported in Table 1. In addition to the various milling products mentioned, which are standard grades, other grades may be obtained by subdividing a grade or by mixing or blending two or more grades. Many of the flours which are placed upon the market are mixtures of two or more stand- ard grades of flour. X> >. loo. Hard Scotch Fife spring wheat, weighing 60 pounds per bushel; screened but not soured. This wheat is representative of the hard spring wheat grown in the North western wheat regions of the United States. No. 154. Entire-wheat flour from hard spring wheat No. 153. This is the product obtained by removing a portion of the bran and grinding the remainder of the grain. It includes the germ and other parts of the offal products which are excluded from the patent grades of flour. This flour is coarser in texture and darker in color than the patent and dear grades. The presence of fine bran particles prevents perfect granulation. Such '"entire-wheat" flour is sometimes called " pulverized graham" or "natural flour." No. 155. Graham flour from hard spring wheat Xo. 153. This consists of the entire wheat kernel including bran, germ, and offal, ground into meal. Graham flour is practically wheat meal; no sieves or bolting cloths are employed in its manufacture, and coarse particles of bran, etc., may be observed in the flour. No. 156. Straight patent flour from hard spring wheat Nc. 153. This includes the first and second patent grades and the first clear or bakers" grade of flour described below. Ordinarily about 72 per cent of the s.reened wheat is recovered as straight patent flour. 11 No. 157. First patent flour from hard spring wheat N<>. L53. This is the bigheert grade of patent flour manufactured. Ordinarilj aboul 56 percent of the screened wheat is recovered as first patent Hour, provided uo straight flour is made. Allot the patent grades of Hour include the middlings which, by the former processes of milling, were not reduced to flour hut were included in the offal products. The presence of the granular middlings gives a relatively high protein content to tin* patent grades of flour. No. 158. Second patent flour from hard spring wheat No. L53. This is similar to firsl patent, but the bread made from it is a little darker in color and the gluten docs not possess quite SO high a power of expansion. The division of the f loin- into first, second, and straight patent grades is based entirely upon mechanical processes. In the higher grades of patent flour the gluten is distinctly different from that in the lower grades. The higher the grade of flour, the greater the power of expansion. It is this quality which enables the flour to absorb a large amount of water and as a result produce a large-sized loaf, and one of good physical properties. No. 1")*). First clear flour from hard spring wheat No. 153. After the first and second grades of patent flour are removed in milling about 12 per cent of first clear grade is obtained. This grade has a high protein content, but the gluten is different in character from that of the first and second patent grades of flour. As already explained, when the first and second patent grades and the first clear grade are blended as one product, the blend is called straight or standard patent flour. No. 160. Second clear or low-grade flour from hard spring wheat No. 153. After the removal of the first and second patent flours and the first clear flour about 5 percent of the original wheat can be obtained as second clear or low-grade flour. This flour is much darker in color than the patent and first clear flours. It contains gluten, with a low power of expansion, and therefore is not so valuable for bread making as the higher grades of flour. Second clear flour is characterized by a high protein content, but for bread making this protein possesses poor physical properties. No. 161. Red-dog flour from hard spring wheat. This is the lowest grade of flour manufactured. It is sometimes used for feeding animals, and occasionally for human food. It is obtained largely from the parts adjacent to the germ or embryo, and is characterized by a high protein content, this protein, however, having different properties from that in the higher grades of flour. It possesses but little power of expansion, and the bread made from this grade of flour is dark in color and poor in quality, at least as regards its physical properties. In the process of milling the wheat germ is not included in the higher grades of flour, because its protein is not composed of gliadin and glutenin. Furthermore, the germ ferments readily, and thus when present in flour has a tendency to render it unsound. Ordinarily from 5 to 8 per cent of the screened wheat is excluded as germ. This is utilized for the preparation of breakfast foods, for blending with other cereal food products, and for other purposes. Frequently, however, the wheat germ finds its way into the shorts and is used for cattle feed. No. 162. Wheat shorts or middlings from hard spring wheat No. 153. About 11.5 to 12 per cent of the cleaned wheat is recovered as shorts, which consist of the fine bran that has been more or less completely pulverized. When the wheat germ is recovered with the shorts, the product is known as middlings. Such "middlings" must not be confused with the middlings obtained when wheat is milled by the old process. As previously stated, the material termed middlings in the old process is now reduced and recovered in the various grades of patent flour. No. 163. Bran from hard spring wheat No. 153. This consists of the coarsely gfc >und episperm or outer covering of the wheat kernel. Ordinarily from 13 to 15 per cent of the cleaned wheat is recovered as bran. 12 No. L64. Entire-wheal bread. This was made of the floor from which sample No. L54 was taken. No. L82. Graham bread. Thia was made of the floor from which sample No. 155 Was taken. Nos. L99 and 217. Straight patent flour bread. In making this bread flour was osed from which sample No. L56 was taken. Nos. 165, 181, 198, and 216. Milk. Mixed milk, used in the digestion experiments. N<». 218. Cleaned soft winter wheat, from Goshen, Ind., prepared for milling, of go<»;> 2.73 12. 15 . 828 2. 62 11.09 .230 2.24 L2.29 .050 2.10 12. 11 .091 2.40 11.27 .660 2. 78 11.23 .830 2. 55 Protein /■< r '■' Hi. 11.7 -.7 11.1 L3.0 17.1 16.4 14.0 13.1 15.0 17.4 15.9 The figures in the table indicate that, while a larger part of the protein is recovered in the flour than is the case with the phosphorus, there is, nevertheless, a parallelism in the proportion of protein and phosphorus in the different milling products. At the Arkansas Experiment Station, Teller a made a very thorough and detailed study of the ash constituents of a sample of locally grown medium hard winter wheat and its milling products. In milling 3,000 pounds of uncleaned wheat, 1.83 per cent was recovered as screenings and 0.33 per cent as tailings, the percentage of milling products being as follows: Patent flour 25.80, straight flour 42, low-grade flour 3.87, dust room contents 1.17, ship stuff 1.13, and bran 23.80. The loss of material in grinding — that is, the material unaccounted for — was therefore only 0.07 per cent. The principal ash constituents and the sulphur and nitrogen in the whole wheat and the different milling products were as follows: Table 3. — Ash constituent* and nitrogen of winter wheat and its milling products. Milling products. Wheat Patent flour Straight flour Low-grade flour Dust room material Ship stuff Bran Total ash.k Per ct. 1.62 .31 .40 .70 2.50 3.08 5.25 Silica. Per ct. 1.04 2.33 1.28 .50 1.34 .49 In total ash. Ferric oxid. Per ct. 0.27 .47 .26 .25 .30 .37 .27 Potash. Per ct. 29.70 38.50 36.31 32.27 30.85 28.03 28.19 Lime. Per ct. 3.10 5.59 5. 65 1. 51 3.53 2.80 2.50 Mag- nesia. Per ct. 13.23 4.39 6.44 9.33 12.90 13.27 14.76 Phos- phoric acid. Per ct. 62.14 48.05 49. 32 53.10 49.94 54.62 52.81 Sul- phur. Per ct. 0.13 .09 .10 .16 .15 .17 .21 Nitro- gen. Pi r a. 1.96 1.54 1.75 2.13 2.17 2.78 2.73 a Arkansas Station Bui. 42, pts. 1. 2. *>This sum includes values which are given for alumina, chlorin, zinc, and sulphur trioxid. which are not quoted in the table. The author regards the values for sulphur present in the different materials as more reliable than those for sulphui trioxid in the ash. owing to a probable volatilization of sulphur in burning to obtain the ash. The other constituents omitted are not of much importance, the alumina and zinc being accidentally present. 16 'Feller points out that about 87.5 per cent of the entire phosphoric acid. 78.5 percent of the potash, and 87.5 per cent of the nitrogen present iu the wheat berry are recovered in the milling products ordinarily used as cattle feeds. As will be seen from the above table, the percentage of phosphoric acid increases as the grade of flour decreases, being least in the patent flour and greatest in low-grade flour, the proportion present in the latter being greater than in any of the milling products except ship stufl; in other words, as shown by these figures, the phosphoric acid content, generally speaking, increases in passing from the center of the wheat berry to the outer layer, the inner portion yielding the fine flour and the outer portion the bran. The table also shows that in the various milling products the propor- tion of nitrogen (and hence that of protein, since the latter is computed by multiplying nitrogen by a constant factor) varies in practically the same way as the phosphorus. The parallelism between protein and phosphorus, which was spoken of above, is borne out by the analytical data quoted, though it does not necessarily follow that the phosphorus present occurs in the true proteids. As a whole, it has been the aim in the experiments conducted at the University of Minnesota to include standard types and varieties of hard and soft wheat flours, milled under different conditions. The differences in the percentages of flour recovered from the wheat used necessarily make slight differences in the composition and character- istics of the grades of flour obtained. The soft wheat products were of different character from the samples of similar products from hard wheat. The hard wheats had been exhaustively milled, as is the usual custom, in one of the large mills of Minneapolis, while the soft winter wheats were ground by mills of smaller capacity using some- what different milling systems, and, as is the general commercial prac- tice, were less exhaustively milled. In general, the flours from soft wheat were somewhat similar to, though not in every respect like those from, hard wheat, because of the differences in the kinds of wheat used and percentages of flour recovered. The graham flour contained the largest percentage of pro- tein, fat, and ash, while the patent grades of flour contained the small- est amounts of these ingredients. A noticeable difference in the mechanical composition of the three grades of soft wheat flour was observed. With the process of milling followed, some granular mid- dlings were left in the offals which would have been recovered in the straight and other grades of flour with more exhaustive milling. This results in a straight-grade flour containing slightly less protein than the product of exhaustive milling, as the granular middlings are rich in this nutrient. The particles or granules of the graham flour were 17 much larger than those of cither the entire-wheat <>r the straight-grade flour. The comparative sizes of granules from graham, entire-wheat, and straight-grade flours ground from soft wheat are shown in the micro-photographs reproduced in Plate I. figs. 1 and 2, and Plate II, fig. L,p. 48. COMPOSITION OF FECES AND URINE OBTAINED IN DIGESTION EXPERIMENTS. The composition of the dry matter of the feces from the digestion experiments is given in Table 4, while Table 5 records the amount. specific gravity, and percentage of nitrogen of the urine. A description of the samples of feces and urine follows: Nos. 178, 199, 180, 195, 196, 197, 213, 214, and 215 represent the feces which were obtained in the digestion experiments with hard spring wheat products. N<.s. 225, 22(1. 227. 233, 2:54. 2:55, 245, 24(5, 247, 252, 25:], 254. 261, 202, and 263, the feces which were obtained in the digestion experiments of 1901-2 with soft winter wheat. Nos. 166-177, 183-194, and 200-212, the urine from the digestion experiments with hard spring wheat products. Nos. 22S, 229, 2:10, 236, 237, 238, 248, 249, 250, 255, 256, 257, 264, 265, and 266, the urine obtained in the experiments with soft winter wheat. Table 4. — Composition of dry matter of feces from digestion experiments with hard and soft wheat breads. Sample No. ITS 179 180 195 196 197 213 214 215 225 226 227 233 234 235 245 246 247 252 253 254 261 262 263 Whence obtained. Experiments with hard wheat Experiment No. 242 Experiment No. 243 Experiment No. 244 Experiment No. 245 Experiment No. 246 Experiment No. 247 Experiment No. 248 Experiment No. 249 Experiment No. 250 Experiments with soft wheat: Experiment No. 309 Experiment No. 310 Experiment No. 311 Experiment No. 312 Experiment No. 313 Experiment No. 314 Experiment No. 315 Experiment No. 316 Experiment No. 317 Experiment No. 318 Experiment No. 319 Experiment No. 320 Experiment No. 321 Experiment No. 322 Experiment No. 323 Protein (NX 6.25) Per <■/ ,ii. 25 37 (HI 2.". Ill (17 Fat. Per ci nt . Carbo- hydrates. Ash. Heat of combus- tion per gram • IcttT- mined. Pi v <-, nt. Per n ,it. 12. 26 34.42 23. 07 7. 45 35.37 28.81 7.44 41.35 26. 21 S. 70 50.16 17.89 5.61 47.59 23. 49 6.41 50.48 21. 11 17.46 25. 02 27. 58 11.44 26. 42 33.58 9.30 36.47 30.29 17.04 45. 15 23. 71 15. 84 38. 92 23.41 9.10 39.40 24.75 5.36 60. 48 19.85 10. 32 55.98 16.94 4.32 56.51 19.11 8.58 43.99 24.82 13.13 38.92 24. 82 15. 26 32. 59 26. 81 5.31 56.28 20. 47 11.65 46.38 20.97 6.00 51.76 23. 57 6.44 57.06 17.00 13.98 51.14 17.02 8.25 52.68 19.94 Calories. 4. 63S 4.070 4.:;.->i •1. U5 3. 960 4.170 4. 720 4.265 4.654 5.030 5.300 4.400 4.340 4. 120 4. 160 5.050 5.160 5.360 4.290 4.410 3.990 4. 220 4. 470 4.170 19047— No. 126—03- 18 Table 5. -Amount, specific gravity, ",, hard "ml soft wheal breads. xpt run, i, ts with Sample Subject 1 66 169 172 175 170 17:; 176 168 171 174 177 183 186 189 192 184 1-7 190 193 185 188 191 194 200 204 207 210 201 206 208 211 206 209 •J 12 229 230 236 237 - - 248 249 256 257 265 Whence obtained. Experiments with hard wheat: Experiment N<>. 242— First day ad day Third day' Fourth day Experiment No. 243— First day Second day Third day Fourth day ™ £££ »««*<» Experiment No. 24 1- First day Second day Third day ' Fourth day Experiment No. 245 — First day Sea >nd day Third day' Fourth day Experiment No. 246 — First day Second day Third day Fourth day Experiment No. 247 — First day Second da y Third day Fourth day Experiment No. 248 — First day Second da v Third day' Fourth day Experiment No. -49 — First day Second day Third day Fourth day Experiment No. 250— First day Second day Third day Fourth day Experiments with soft wheat: Experiment No. 309 Experiment No. 310 Experiment No. 311 Experiment No. 312 Experiment N< >. 313 Experiment No. 314 Experiment No. 315 Experiment No. 316 Experiment No. 317 Experiment No. 318 Experiment No. 319 Experiment No. 320 Experiment No. 321 Experiment No. 322 Experiment No. 323 L, 368.0 1,350.0 1. 163.6 1,326.0 L, 805,0 2.112.0 2,298.0 2,248.0 1,991.0 1,720.0 1,679.0 1,947.0 1 . 27i i. II 1.210.0 1.212.0 1.102.0 1,943.0 1 . 732. II 2, 188. 2,368.0 1,851.0 1,581.0 1,614.5 1,338.0 1,124.0 1.077.0 1,068.0 1,110.0 1, 943. 1,698.0 2,182.0 2. 023. U 1.123.0 1.242.0 1,601.0 2. 463. 6.023.1 4,296.2 4. 486. 2 5, 652. 9 5,201.7 4,115.6 7,317.4 6, 556. 6 1.747.6 -- 6.910.1 5,476.6 •">. 210.1 1,532.0 1.026 1.023 1.027 1.029 1.016 j 1.016 1.015 1.017 1.020 1.021 1.025 1.028 I 1.030 j 1.030 I 1.030 1.028 1.015 1.015 1.015 1.014 1.024 1.025 ' 1.027 1.027 1.027 1.031 1.030 1.029 1.014 1. 015 1.015 1.014 1.028 1.026 1.022 1.016 L5fi 1.4"- 1.74 .95 1.00 1.3n 1.41 1. 72 1.4-. 1.82 l.7y 1.84 1.88 1.03 1.01 1.72 1.7-S 1.91 1.77 2.10 1.90 2.04 1.02 1.00 .97 .97 1.82 1.81 1.56 1.07 1.016 1.10 1.020 1.50 1.019 1.31 1.019 1.21 1.020 1.41 1.02-2 1.4s 1. 016 1.19 1.019 1.41 1.020 1.39 1.016 1.07 1.020 1.47 1.021 1.61 1.020 1.41 1.020 1.16 1.022 1.80 EXPERIMENTAL METHODS. The methods followed in all of the experiments here reported are practically identical with those described in detail in the previous publication" already referred to. and need only be briefly outlined. The bread from the different sorts of flour was eaten with milk: the amount of cither was not limited, but the quantities eaten at each meal were recorded. The separations of the feces were made by means of I. B. Dept A-r.. Office of Experiment Stations Bui. 101. 19 charcoal taken with a meal of bread and milk, which gives feces of a characteristic color and consistency. The digestibility of the nut rients of the diet as a whole was taken as the difference between the amounts in the food and those in the feces, no attempt being made to determine the metabolic products of the feces.'' In order to compute the digestibility of the nutrients of the bread alone, it was assumed that 97 per cent of the protein. 95 per cenl of the fat, and 98 per cent of the carbohydrates of milk were digested. The undigested nutrients of the milk as calculated by the use of these factors subtracted from the nutrients of the total feces give the esti- mated undigested nutrients from bread, which, subtracted from the total nutrients of the bread, give the digestible nutrients in bread. The latter, divided by the total nutrients in the bread, give the coeffi- cients of digestibility of bread alone. The values used for the digestibility of the nutrients of milk have been deduced from the results of a large number of digestion experi- ments with milk. P^ven if, in the experiments here reported, the diges- tibility of the milk nutrients varied from these assumed coefficients, the figures for the digestibility of the nutrients of the different kinds of bread are still strictly comparable because the same factors for milk were used in all cases. As has been already explained, 6 the energy of the estimated feces from bread alone was computed by proportion from the energy of the total feces. The ratio of the heat of combustion of the bread feces as computed b}- factors to the actual energ} T was assumed to be the same as the ratio of the computed energy- of total feces to the heat of combustion as determined. Although the energ}^ of the urine was determined, in the calculation of the availability of the energy of the total food and of the bread alone, it was assumed, for the sake of uniformity with experiments previously reported, that 1.25 calories of energ} T would appear in the urine for every gram of digestible protein in the total food or in the bread alone. For the sake of making an approximate estimate of the available energy in those experiments where the digestibility of the bread fat could not be computed, it was assumed that 90 per cent of «It should be observed that the results thus obtained do not represent actual digestibility. The true digestibility could be found by subtracting from the ingredi- ents of the food the corresponding ingredients of the feces that come only from undi- gested portions of the food. But no satisfactory method has been found for separating these from the metabolic products in the feces, which consist largely of the residues of the digestive juices that have not been reabsorbed. These latter represent the cost of digestion as expressed in terms of food ingredients. What the results of these experiments do represent, therefore, is the proportions of the food, or of the several ingredients, that are available to the body for purposes other than digestion itself. In accordance with common usage, however, the term digestibility, which indicates the apparent digestibility, has been employed here; the term availability is some- times used to express the same idea. &U. S. Dept. Agr., Office of Experiment Stations Bui. 101, p. 22. 20 the fat of the bread was digestible. The results thus found would probably be below rather than above what was actually the case. As in the preceding experiments, the balance of income and outgo of nitrogen was learned by determining the daily amounts ingested in the food and excreted in the urine and feces. In the experi- ments with soft winter wheat in 1901-2 determinations were also made of the phosphoric acid in the samples of food, feces, and urine. Such data, however, are reserved for further study. The particular difference between the digestion experiments given here and those formerly reported is in the length of the experimental period, this being four days long here and only two in the earlier experiments. The longer experimental period is believed to be pref- erable, because it is generally considered that there is less danger of error due to uncontrollable factors that may vitiate the results in a short digestion period. As is well known, the results obtained from a digestion experiment are not absolute, but only relative. But inasmuch as in the diges- tion experiments reported in this bulletin the object is to deter- mine the relative rather than the absolute digestibility of three different kinds of bread, it is believed that the results obtained are satisfactory for this purpose, because whatever error may be intro- duced in one experiment is introduced alike in all of an}* given series. since the conditions were kept uniform throughout the series. While the results of a single digestion experiment are open to criticism, the results obtained from a series of experiments are much less so and are of value in determining whether one food is more digestible than another under similar experimental conditions. Hence in discussing the results obtained from these digestion experiments they are con- sidered in relation to one another rather than alone. DETAILS OF THE DIGESTION EXPERIMENTS WITH BREAD FROM DIFFERENT GRADES OF HARD SPRING WHEAT FLOUR. The details of the digestion experiments with hard wheat products are given in the following pages. Nine digestion experiments, each of four days* (or twelve meals') duration were made with three different subjects. In every case the diet consisted of bread and milk, and all of the experiments were conducted in the same manner, except that bread made from a different kind of Hour was used in each series. In making the bread no shortening or milk was used, but simply yeast, flour, salt, and water. The subjects were university students who spent from three to four hours each day at light muscular work out of doors. All had served as subjects in former digestion experiments and were thoroughly familiar with the requirements of such work. The experiments were practically made in triplicate — that is, the same kind of an experiment was made with each of three subjects at 21 the same time. TheorderiD which they were conducted was as follows: The firsl scries of experiments (with entire-wheat bread) extended from April 17 to April l>0, inclusive; the second series (with graham bread) from April 23 to April 26, inclusive; and the third series (with bread from standard patent Hour) from May 1 to May 4. Inclusive. The experiments were taken up in this order because of the difficulty experienced in previous experiments with a graham bread and milk diet. It was believed that the investigation could he conducted to better advantage by having the graham bread experiment between the others, lather than at the beginning or close of the series. The four days* diet of graham bread and milk caused a slight irritation of the digestive tract and a slight attack of gastritis with two of the subjects. The following tables, Nbs. 6 to 11, and the accompanying data show the kind of food consumed, the subject experimented upon, the body weight at the beginning and at the close of the experiment, and the date and duration. Then follow statistics of the total nutrients in the food and the feces, and the heat of combustion of each, and after each of the tables statistics are given of the income and outgo of nitrogen during the experiment. DIGESTION EXPERIMENT NO. 242. Kind <>f food. — Milk, and bread made from entire-wheat flour. Subject. — University student No. 1, 22 years old, employed about four hours per day at manual labor. Wright. — At the beginning of the experiment, 168 pounds; at the close, 168 pounds. Duration. — Four days, with twelve meals, beginning with breakfast April 17, 1901. Table 6. — Results of digestion experiment No. 242. Sample No. Weight of material. Protein. Fat. Carbo- hydrates. Ash. Heat of combus- tion. 164 165 Food consumed: Bread Milk Grams. 3, 550. 9, 950. Grams. 330.9 323.4 Grams. 6.7 378.1 Grams. 1,730.7 431.8 Grams. 27.3 79.6 < 'ainrits. 8,998 6 965 Total 654.3 384.8 2, 162. 5 106.9 I 15,963 Feces (water free) Estimated feces from food other than bread 17* 214. 64.7 9.7 26.2 73.7 8.6 49. 4 992 Estimated feces from bread 55.0 66. 1 Total amount digested 589.6 275 9 358 6 2, 088. 8 1,665.6 57.5 14.971 Estimated digestible nutrients in bread Coefficients of digestibility of total food Per cent Per cent. 90.1 .S3. 4 Per cent. 93.2 l'i r a nt. 96.6 96.2 Per a nt. 53.8 Per cent. 93.8 Estimated coefficients of diges- tibility of bread <« 93. Proportion of energy actually available to body: In total food..* 88.2 In bread alone a 89.1 a Estimated on the assumption that 90 per cent of the fat in the bread is digestible. 22 During this experiment the subject eliminated 5,508 grams urine, containing 88.42 grams nitrogen. The average nitrogen balance per dav was therefore as follows: Income in food. 27.47 grams; outgo in mine. 22.10 grams and in feces, 2.59 grams, implying a gain of 2.78 grams nitrogen, corresponding to 17.4 grams protein. DIGESTION EXPERIMENT NO. 243. KmdoffoocL Milk, and bread made from entire-wheat flour. Subject. — University student No. 2, 22 years old, employed about four hours per day at manual labor. Wright. — At the beginning of the experiment, 150 pounds; at the close, 155 pounds. I >>i ration. — Four days, with twelve meals, beginning with breakfast April 17, 1901. Table 7. — Results of digestion experiment No. ./■/'•/. Sample No. Weight of material. Protein. Fat. Carbo- hydrates. Ash, Heat of combus- tion. 164 Food consumed: Grams. 3. 101. C 12, 310. Grams. 289.0 400.1 Grains. 5.9 467.8 Grams. 1,511.8 534.3 Grams, 23.9 Calories. 7.8K0 165 Milk 98.5 1 8,617 Total Feces ( water free) Estimated feces from food other than bread 689. 1 473.7 2,046.1 122. 4 16, 477 179 180. 51.1 12.0 13.4 63. 7 10.7 51.9 733 Estimated feces from bread 39.1 53.0 Total amount digested 638.0 249.9 460. 3 1,982.4 1. 158.8 70.5 15,744 Estimated digestible nutrients in bread Coefficients of digestibility of total food Per cent. Per cent. 92.6 86.5 Pt r <■> ut. 97.2 96.9 96.5 Pun nt. Percent. .".7 6 Estimated coefficients of digest- "90.4 Proportion of energy actually available to body: ' In total food. .". 90.7 In bread alone a 90.0 1 « Estimated on the assumption t hat 90 per cent of th e fat in th e bread is digestible During this experiment the' subject eliminated 8,463 grams urine, containing 80.95 grams nitrogen. The average nitrogen balance per day was therefore as follows: Income in food. 28.68 grams; outgo in urine, 20.21 grams, and in feces, 2.09 grams, implying a gain of 6.35 grams nitrogen, corresponding to 39.7 grams protein. 23 DIGESTION EXPERIMENT NO. 244. Kind of food. Milk, and bread made from entire-wheat flour. Subject. University student No. 3, 21 years old, employed about four hours per day at manual labor. Weight. — At the beginning of the experiment, L61 pounds: at the close. L60 pounds. Duration. Four days, with twelve meals, beginning with breakfast April IT. UXH. Table 8. — Results of digestion experiment No. 244> Sample No. Weight of material. Protein. Fat. Carbo- hydrates. Ash. Heat of combus- tion. 164 Food consumed: Grams. 3, 760. 14,843.0 Grams. 350.4 482.4 Grams, 7.1 564.0 Grams. 1,833.1 644.2 Oram*. 28.9 118.8 Calorie*. 9,530 165 Milk .... 10, 390 Total 832.8 571.1 2,477.3 147.7 19, 920 180 215. 1 53.8 14.5 16.0 88.9 12.9 56.4 936 Estimated feces from food other Estimated feces from 39.3 76.0 Total amount digested 779.0 311.1 555.1 2,388.4 1, 757. 1 91.3 18,984 Estimated digestible nutrients in bread Coefficients of digestibility of total food Per cent. Per cent. 93.5 88.8 Per cent. 97.2 Per >■' nt. 96.4 95.9 Per cent. 61.8 Per cent. 95.3 Est i mated coefficients of digest- ibility of bread « 94. 3 Proportion of energy actually available to body: In total food 90.4 In bread alone u90.2 . Sample No. Weight of material. Protein. Pat Carbo- hydrates. ash. Heat of combus- tion. 182 Pood consumed: Bread Gram*. 3, 342.0 LO, 207.0 Urn ins. 318.8 319.5 Gram*. 9.7 408. 3 Grams. 1,540.7 480.8 Grams. i»;. :. Calories k 8.837 181 Milk 90.8 7.til4 Total (538.3 418.0 2,021.5 137.3 15,951 196 300. 1 69.8 9.G 26. 1 ■JO. 4 150. 5 9.fi 53.7 1,325 Estimated fecesfromfood other 302 Estimated feces from GO. 2 5.7 140.9 1,023 568. 5 258.6 391.9 1,871.0 4.0 1,399.8 83.6 14,626 Estimated digestible nutrients 7,314 Coefficients of digestibility of Per cent. Per cent. B9. 1 81.1 Per <■< nt. 93.8 41 2 Per <■> ut. 92.6 90.9 Per cent. 60.9 Per cent. 91 7 Estimated coefficients of digest- ^7 7 Proportion of energy actually available to body: 87.2 83.9 During this experiment the subject eliminated 4,794 grams urine, containing 87.79 grams nitrogen. The average nitrogen balance per day was therefore as follows: Income in food, 26.74 grams; outgo in urine. 21.9.5 grams, and in feces 3.79 grams, implying a gain of 1 gram nitrogen, corresponding to 6.3 grams protein. DIGESTION EXPERIMENT NO. 246. Kind of food. — Milk, and bread made from graham flour. Subject. — University student No. 2. Weight. — At the beginning of the experiment. 154 pounds; at the close, 152.7 pounds. Duration. — Four days, with twelve meals, beginning with breakfast April 23, 1901. Table 10. — Results of digestion experiment No. 246. Sample No. Weight material. Protein. Fat. Carbo- hydrates. Ash. Heat of combus- tion. 182 Fooft consumed: Bread Grams. 2,855. 10,568.0 Grams. 272. 4 330.8 Grams. 8.3 Grams. 1 Rlfi 2 Grams. 39.7 94.1 Oaiones. 7,123 181 Milk 422. 7 4^7. 8 7,883 Total 603. 2 431.0 1,814.0 133. S 15, 006 Feces ( water free) 196 259.0 60.4 9.9 14.5 123 3 60.8 1 026 Estimated feces from other than bread food 10 Estimated leces lrom .50. 5 113.3 Total amount digested Estimated digestible nut in bread 542. S 221. 9 416 5 1.690.7 1,202.9 73.0 13 980 riciits 25 Table 10. — Results of digestion experiment No. ."/'•- Continued. Bample No. Coefficients oi digestibility of total food Estimated coefficients of diges tibility of bread Proportion of energy actually available to body: In total food In bread alone Weight material, l'< r <■< ni. Protein. Fat. Percent. Percent. 90.0 96.6 SI. 5 Carbo hydrates, l'i r r, at. 98.2 91.4 ash. Heal oi «C (II l 1 .11- IlMl,. i'< r -•' hi. 4.6 Per a nt. "88.9 a 86.1 ni. 93.8 92.2 Per cent. 63.9 Per cent. 93.8 Estimated coefficients of diges- tibility of bread «90. 3 Proportion of energy actually available to body: In total food 89.2 In bread alone a 86 2 a Estimated on the assumption that 90 per cent of the fat in the bread is digestible. 26 During this experiment the subject eliminated 6,385 grams urine, containing L07.13 grams nitrogen. The average nitrogen balance per day was therefore as follows: Income in food. 30.01 grams; outgo in urine 26.78 grams, and in feces. 2.32 grams, implying a gain of 0.91 grams nitrogen, corresponding to 5.7 grams protein. DIGESTION EXPERIMENT NO. 248. Kmd of food. Milk, and bread made from straight patent Hour. Subject. — University student No. 1. Weight. — At the beginning of experiment. 164 pounds; at the close, It 14 pounds. Duration. — Four days, with twelve meals, beginning with breakfast May 1, 1901. Table 12. — Results of digestion experiment 1 Vo. 248. Sample] *«§*' V, . (JI ISO * 1 material. Protein. Fat. Carbo- hydrates. Heat of Ash. combus- tion. Food consumed: 199 Bread 19S Milk Total Grams. 2,575.0 10,583.0 Grams. 248.0 321.7 Grams. 1.0 404.3 Grams. 1.314.9 509.0 Grams. Calorie*. 12.9 6,680 78.3 J 7.715 569.7 405. 3 1,823.9 91.2 14,395 213 152. 45. 5 9. G 26.5 38.0 20.2 10.2 41.9 717 Estimated feces from food other than bread 309 Kstima t ed feces from bread T< »tal amount digested 35.9 27. 8 524. 2 ,,,, 378.8 1,785.9 1,287.1 4^. 3 13, 678 Estimated digestible nutrients in bread Coefficients of digestibility of total food . Per cent 92.0 Per cent. 93.5 1>> r cent. 97.9 97.9 • 54 1 Per cent. 95.0 Estimated coefficients of digest- a 94.8 Proportion of energy actually available to body: ' In total food .* 90.5 a 90. 9 " Estimated on the assumption that 90 per cent of the fat in bread is digestible. During this experiment the subject eliminated 4.378 grams urine, containing 85.44 grams nitrogen. The average nitrogen balance per day was therefore as follows: Income in food. 23.79 grams: outgo in urine. 21.38 grams, and in feces, 1.82 grams, implying a gain of 0.59 gram nitrogen, corresponding to 3.7 grams protein. DIGESTION EXPERIMENT NO. 249. Kind of food. — Milk, and bread made from straight patent flour. Subject. — University student No. 2. Weight.— At the beginning of the experiment, 152 pounds; at the close, 15H pounds. Duration. — Four days, with twelve meals, beginning with breakfast Mav 1, 1901. 27 Table L3. — Results of digestion experiment No. ./'■'. Sample Ho. Weight Of material. Protein. Pat. I hydrates. ash. Ibat Of combue tioli. 199 Food consumed: Bread drums. 2, 790. ll.717.it Grama. 268. 7 Grams. L2 H7. 6 Grams. 1. 124.6 Grams. I'nlnrii*. 198 Milk Touil m 9 lis. s 100.6 15,779 'Ml 146. 8 41.9 10.7 16.8 38.8 11.3 49.3 626 Estimated feces from food other Estimated feces from 31.2 27.5 583.0 237.5 432.0 1,949.4 1,397.1 51.3 15, 153 Estimated digestible nutrients Coefficients of digestibility of Per cent. Per cent. 93.3 88.4 Per cent. 96.3 Per cent. 98.1 98.1 Per cent. 51.0 • 96.0 Estimated coefficients of digest- «95.5 Proportion of energy actually available to body: 91.4 |"" «91.4 « Estimated on the assumption that 90 per cent of the fat in the bread is digestible. During this experiment the subject eliminated 7.840 grams urine, containing 77. 52 grams nitrogen. The average nitrogen balance per (lav was therefore as follows: Income in food, 26.05 grams; outgo in urine, 19.38 grams, and in feces, 1.68 grams, implying a gain of 4.99 grams nitrogen, corresponding to 31.2 grams protein. DIGESTION EXPERIMENT NO. 250. Kind of food. — Milk, and bread made from straight patent flour. Subject* — University student No. 3. Weight.— At the beginning of the experiment. 152 pounds; at the close, 155 pounds. Duration. — Four days, with twelve meals, beginning with breakfast May 1,1901. Table 14. — Results of digestion experiment No. 250. Sample No. Weight of material. Protein. Fat. Carbo- hydrates. Ash. Seal oi combus- tion. 217 •Jit; Food consumed: Bread Milk Grams. 3,080.0 13,055.0 Grams. 300.0 , 441.3 Grams. 8.0 541.8 Grams. 1,605.3 596.6 drams. . 15.7 99.2 Calories. - 9,713 Total 741.3 549.8 2,201.9 114.9 17, 865 215 167.0 40.0 13.2 15.5 60. 9 11.9 50.6 777 Estimated feces from food other than bread Estimated feces from 26.8 49.0 Total amount digested .... 701.3 273.2 534.3 2, 141. 1,556.3 ■ - 64.3 17,088 Estimated digestible nutrients in bread 28 Table 14. — Results of digestion experiment No. 250 — Continued. Sample No. Weight of material. Protein. Fat. Carbo- hydrates. Ash. Heat of combus- tion. Coefficients of digestibility of Per cent. Per cent. 94.6 91.1 Per cent. 97. 2 Per cent. 97.2 97.0 Per cent. 56.0 Per cent. 95 7 Estimated coefficients of diges- tibility of bread "94.5 Proportion of energy actually available to body: 90.8 "90.3 " Estimated >>n the assumption that 90 per cent of the fat in the bread is digestible. During this experiment the subject eliminated 6,439 grams urine, containing 94.25 grams nitrogen. The average nitrogen balance per day was therefore as follows: Income in food, 30.70 grams; outgo in urine, 23.56 grams, and in feces, 1.60 grams, implying a gain of 5.60 grams nitrogen, corresponding to 35.0 grams protein. SUMMARY OF RESULTS OBTAINED WITH HARD SPRING WHEAT PRODUCTS. The following tables summarize the results of the digestion experi- ments with hard spring wheat products reported in the foregoing pages. The results are given for the whole ration in Table 15 and computed for the different sorts of bread alone in Table 16. For purposes of comparison, the results obtained in previous experiments in this laboratory are also included, as well as the average digestibility of the different kinds of bread as shown by the result of all the experiments. Table 15. — Summary of digestion experiments with hard spring wheat; digestibility of nutrients and availability of energy of total food. No. wo - 242 243 244 245 246 247 248 249 250 Kind of food. Milk and entire wheat bread do do Average of 3 Average of 3 ( 1899-1900) . Average of 6 Milk and graham bread do do Average of 3 Average of 3(1899-1900). Average of 6 Milk and white bread (standard patent | do ....do Average <»i 3 Average of 3 (1899-1900) Average of 6 Protein. Per cent. Fat. hSSe, *»™ Per cent. 93.2 92.6 ! 97.2 93.5 97.2 92.1 89.7 89.1 90.0 91.9 90.3 88.2 89.3 Per cent. 96.9 96.4 95.9 91.7 93.8 93.8 96.6 96.6 95.7 91.1 93.4 Per cent. 89.2 90.7 90.4 96.6 95.1 95.8 92.6 93. 2 93.2 91.1 92. 2 92.0 93.3 94.6 93.5 96.3 97.2 97.9 98.1 97.2 93. 3 91.4 9-2.4 95.7 92.4 9,5 97.7 97.6 97 7 90.1 88.5 89.3 88.3 86.0 87.2 90.5 91.4 90.8 90.9 90.3 90.6 29 Table 1<>. — Summary of digestion experiments with hard spring wheat; digestibility of nutrients and availability of energy of bread alone. Expert- IIH'Ill No. 242 2 13 244 245 246 247 248 249 250 Subjed No Kind of [ood. Entire wheal bread ....do ....do Average of 8 Average of 8 (i.sw-1900) Average of 6 (Iralmm bread. do ....do Average of 3 Average of 3 (1899-1900) Average of 6 White bread (standard patent). do ....do Average of 3 Average of 3 (1899-1900) Average of 6 Protein. p< /■ cent. 83. I 86. 6 88. 8 so. •_> 80. 1 S3. 3 Carbo- hydrates. i'i r cent. 96. 2 96.5 96. 9 81.1 81.5 85.9 82.8 77.6 80.2 85. 5 88.4 91.1 88.3 85.3 86.8 96.2 94. 1 95. I 91. I 92, 2 91.5 88.4 90.0 97.9 98.1 97.0 97.7 97.5 97.6 Energy. Per a nt. 89. 1 90.0 90. 2 s-.t. s 87. 6 88.9 85. 1 86.2 85. 1 80.7 82.9 90.9 91.4 90.3 90.1 90.5 It will be observed that the average coefficients of digestibility of the protein and carbohydrates and of the available energy in the ration consisting of milk and bread made from straight patent flour ground from hard spring wheat were larger than in the rations of milk and entire-wheat bread or milk and graham bread from the same lot of wheat. Considering the calculated results for bread alone, in the experiments here reported it appears that in the graham bread the average digestibilit}- of the protein is 82.8 per cent; of the carbolry- drates, 91.5 per cent, and the available energy is 85.1 per cent. The digestion coefficients for the graham bread are lower than for either the entire-wheat bread or the straight patent flour bread. In the case of the bread from entire-wheat flour 86.2 per cent of the protein was digested, and in the straight patent flour bread 88.3 per cent, while 96.2 per cent of the carbohydrates in the entire-wheat flour bread and 97.7 per cent of those in the bread from the straight patent flour were found to be digestible. An examination of the tables also shows in each of the series a range of from 4 to nearly 6 per cent in the digestion coefficients of each of the nutrients. This is probably due to differences in the digestive powers of the three subjects. Thus, for example, subject No. 3 digested the bread made from straight patent flour, entire-wheat flour, and graham flour more completely than either subject No. 1 or No. 2. While individual differences are observed in the three series of experiments, in every case it appears that each subject digested the nutrients in the straight patent flour bread more completely than the nutrients in either the entire- wheat bread or the graham bread. 30 Hence the results for the average digestibility in the different scries of experiments arc strictly comparable. The tables also compare tin 1 results of the experiments reported in tins bulletin and those formerly reported." It will be observed that although the digestion coefficients are somewhat larger in the experi- ments here reported than in those of ls ( .*!»-l ( .M>o, there is a general similarity of results. In both series the nutrients of the bread from standard patent flour are the most and those of graham the least digestible, the entire-wheat flour bread being between the two. These experiments are regarded as strictly comparable. Considering the two years' investigations as a whole, six subjects wen 1 employed and eighteen separate digestion experiments were made. Table 1(> gives the average digestibility of the nutrients and availa- bility of the energy in the three kinds of bread as shown by the results of the two series. It is believed that these figures show, with a fair degree of accuracy, the comparative digestibility of the protein and carbohydrates and availability of energy in bread made from the three kinds of flour when milled from the same lot of hard spring wheat and consumed under similar conditions. The results, considered as a whole, show that the protein in the straight patent flour bread is 6.i) per cent more digestible than that of the graham bread, while the carbohydrates are 5.6 per cent more digestible. The amount of avail- able energy in the straight-flour bread is also greater by 7.5 per cent than that in the graham bread. In Table 17 the total and digestible protein and carbohydrates and total and available energy in the three different kinds of flour as milled are given. These values for digestible nutrients and available energy were obtained by multiplying the percentage of total nutrients and energy by the coefficients given in Table 17. Table 17. — Percentages <>f digestible protein and carbohydrates, and a callable energy in entire-wheat, graham, and straight patent flours as milled. Protein (Nx5.70). Glade of flour from hard spring wheat. Straight patent Entire wheat .. (iraliam Di bfe Sti " Per a nt. 13.60 13. 72 14.21 Prr ft nt. 12. 01 11.83 11.77 Carbohydrates. Energy per gram. Total. Per cent. 72. 04 70.09 68. 55 Digesti- ble. Per cent. 70.31 67.43 62. 62 Total. Per cent. 3.861 3.877 3.971 Avail- able. Per cent. 3.510 3.481 3. 379 There was a somewhat larger amount of digestible protein in the straight patent flour than in either the graham or entire-wheat flour. In the straight patent flour there was 70.31 per cent of digestible carbohydrates, in the entire-wheat flour 67.43 per cent, and in the «U. 8. Dept. Agr., Office of Experiment Stations Bui. 101, p. 33. 31 graham flour 62.62 percent; that is. the carbohydrates of the straight patent flour were much more digestible than those of either the entire wheat or graham Hour. The amount of available energy of the si might patent' Hour is also Larger than that of either the graham or entire- wheat flour. On comparing the figures in this table with those previously reported it will be observed that the results for protein here given are higher. This is due to two facts already pointed out, namely, that the per- centage of protein in the wheat employed in these experiments was higher, and the coefficients of digestibility were larger. The signifi- cance of the results, however, is the same in both eases. Briefly stated, the results of all of the experiments with hard spring wheat show that the digestible protein and carbohydrates, as well as the amount of available energy, are greater in the standard patent flour than in either the graham or entire-wheat flour. No marked variations in the balance of income and outgo of nitrogen were observed in the different periods except such as were due to differences in the amounts consumed. In other words, judged by the data regarding the metabolism of nitrogen, the three sorts of breads served the body equally well. The results of these experiments confirm those of earlier work with hard-wheat flours, and show that when breads made from straight patent flour, entire-wheat flour, and graham flour, milled from the same lot of hard spring wheat, are fed under uniform experimental conditions to men, there is a larger amount of digestible protein and carbohydrates and available energy in the patent flour than in either the entire- wheat or graham flour, although judged by composition the graham flour contains the most and the patent flour the least total protein. The greater digestibility of the protein and carbohydrates of the patent flour is regarded as due in part at least to the fineness of division of the flour particles, or, in other words, to the fact that a considerable portion of the nutrients in the graham and entire-wheat flours are present in comparatively large particles, which resist the action of the digestive fluids and so escape digestion. It has also been suggested that the cell walls in the layer of the grain directly under the bran are more resistant to digestive juices than the walls of cells in the interior of the kernel (see pp. 48, 49). Thus while there is actually somewhat more protein, pound for pound, in graham or entire-wheat than in patent flour, the body obtains less protein and energy from the coarser than it does from the finer flour, and whatever is gained in composition by adding the bran or germ is offset by the loss in digestibility. «U. S. Dept. Agr., Office of Experiment Stations Bui. 101, p. :;.",. 32 DETAILS OF THE DIGESTION EXPERIMENTS WITH BREAD FROM DIFFERENT GRADES OF SOFT WINTER WHEAT FLOUR. In order to determine whether the results obtained with oread from hard-wheat flours would be the same with Hours from wheat of a dif- ferent character, fifteen digestion experiments were made with bread from graham, entire-wheat, and standard patent flours milled from soft winter wheat. The results of these experiments are reported on the following pages. Two sets of experiments were made. In one set. comprising the first six of the following experiments, the flours used were prepared from the same lot of Indiana soft winter wheat by a milling company of ( roshen, Ind. Only two kinds of flour were used in these six experi- ments, one being a standard patent grade similar to but not quite the same as the same grade of flour used in the experiments with hard wheat: the other was a so-called entire-wheat flour, but was somewhat coarser than this grade of flour prepared from hard wheat. In the second set of experiments three grades of flours were used, all ground from the same lot of Michigan soft winter wheat by a milling company of North Lansing. Mich. The experiments were made by the same methods as were followed in earlier work with hard-wheat flours. The experiment proper was preceded by a preliminary meal of bread and milk, charcoal being used to mark the separation of the feces. The experimental period con- tinued three days in the experiments with the Indiana flours, and four days with the Michigan flours. The subjects were young men in good health, designated as Nos. 1. 2, and 3. They were employed at farm Labor, office, and university work. One subject. No. 1. had been employed in the digestion work of 1900 and 1901 as subject No. 3. The subjects were allowed a diet of bread and milk, unrestricted as to amount, the quantities consumed at each meal being carefully weighed. The different series of experiments in which graham, entire-wheat. and straight-grade flours were used were alike in all respects except as regards the bread. The four days' diet of milk and graham brea'd proved to be rather laxative. It was observed that the subjects who were employed at the severest labor had a decided preference for the bread made from the straight and mixed grade flours, while the one employed at office and university work did not have so pronounced a preference. In no case was the graham bread preferred. Tables 18 to 32 record the data of the several digestion experiments. DIGESTION EXPERIMENT NO. 309. Kind of food. — Milk, and bread made from straight-grade flour. Subject. — Man No. 1; age. 25 years: employed at office work. IT ight. At the beginning of the experiment. 161.25 pounds; at the close, 162 pounds. 33 Duration* — Three days, with nine meals, beginning with breakfast April 9, 1902. Table is. — J:, suits of digestion > vperinn • ! Bampfc ' No. Weight ol material. Protein. Fat. Carbo- hydrates. Ash. combus- tion. 228 22 1 Pood oonsumed: Bread Milk Total Feces ( water free) Grams. 2,950.0 9,850.0 Grams. 236.3 826.0 Grams. 17.7 431. 1 Grams. 1,613.9 445.2 <, nuns. 16.0 77.8 Calories. 7.994 562. 3 419.1 1.959.1 92. B 15.677 225 166.0 23. 4 28. 3 74.9 39.4 ft35 Estimated feces from food other 317 Estimated feces from bread Total amount digested Estimated digestible nutrients in bread Coefficients of digestibility of total food 13.6 6.7 66.0 188 538. 9 222. 7 120. 8 11.0 1.884.2 1.447.9 53.4 14, 842 7, 506 l'i r a ut. Per cent. 95.8 94.2 l'i r c> ut. 93.7 62.1 Per cent. 95.6 Per cent. 57. 5 Per cent. 94.7 Estimated coefficients of diges- tibility of bread 93.9 Proportion of energy actually available to body: 90.4 In bread alone 90.4 During this experiment the subject eliminated 6,023 grams urine, containing 66.25 grams nitrogen. The nitrogen balance per day was therefore as follows: Income in food. 31.20 grams: outgo in urine. 22. <>S grams, and in feces, 1.25 grams, implying a gain of 7.87 grams nitrogen, corresponding to 19.2 grams protein. DIGESTION EXPERIMENT NO. 310. Kind of food. — Milk, and bread made from straight-grade flour. Subject. — Man No. 2: age. 25 years: university student: employed at average farm labor four hours per day. Weight. — At the beginning and close of the experiment. 163.75 pounds. Duration. — Three days, with nine meals, beginning with breakfast April 9, 1902. Table 19. — Results of digestion experiment No. SlO. Sample No. Weight Oi Protein, material. v,.t Carbo- , h Fat - hydrates. Ash ' Heat of combus- tion. 223 Food consumed: Bread Grams. 2, 860. 7,850.0 Grams. 229. . 259.8 Grams. Gra s. Grams. 17.2 1,467.7 14.6 343.8 854.8 62.0 Calories. 224 Milk 6. 123 Total 488.8 i 361.0 1.822.5 76.6 13,874 Feces ( water free) 226 147.0 32.1 ' 23.3 57.2 34.4 77s) Estimated feces from food other than bread 7. 8 17.2 7.1 ' 1 287 Estimated feces from bread 24.3 6. 1 50. 1 492 19017— No. 126—03- 34 Table L9. — Results of digestion < rperimeni No. S10 — Continued. Sample No. Weighl of Protein, material. Fat. Carbo- hydrates. Ash. Bea1 of combus- tion. j Orams. Grams. Total amount digested 156. 7 Estimated digestible nutrients in bread Jul. 7 Qrams. drains. 337. 7 1 u.o i . 417.*; Grams. Calories. 1J.-' 13,095 259 Coefficients of digestibility of Percent. total food Estimated coefficients of ■> nt. 93. 6 89. 5 Per <■> ut. 97.1 Per cent. 92.1 90. 3 Per ct nt. 56. i Per cent. Estimated coefficients of digest- ibility of bread follows: Income in food, 27.48 grams; outgo in urine. 20.30 grams, and in feces, 2.W grams, implying a gain of 4.24 grams nitrogen, corresponding to 26.5 grams protein. DIGESTION EXPERIMENT NO. 315. Kind of food. — Milk, and bread made from straight Hour. Subject. — Man No. I. as in experiment No. 309. Weight. — At the beginning and close of the experiment, 106 pounds. Duration.— Four days, with twelve meals, beginning with breakfast April 28. 1902. ■Table 24. — Results of digestion experiment No. 315. Sample No. : Weight ' ol material. Protein. M. Carbo- hydrates. Heat of Ash. combus- tion. 244 243 Food consumed: Grams. Bread 3,615.0 Milk U,750.u Grams. 274.4 351.3 Grams. 13.7 180. 6 Grams. 1,970.3 565. 2 Grams. Calories. 17.7 y.435 90.5 B,719 Total 625. 7 494.3 2.541.5 108.2 is, 154 245 Feces i water free | 132. 29. 8 ,„..-, 11.3 11.3 32.8 667 Estimated feces from food other Bstlmatedfecesfrombread 19.3 16. 8 Total amount rligested 595.9 253. 1 4S3. 2, 183. 4 1 929 5 75.4 17,487 Estimated digestible nutrients Coefficients of digestibility of Percent. total food Per cent. 95. 2 93.0 Ptr cent. 97. 7 - 69.7 96.3 Estimated coefficient of diges- tibility of bread ' a 97. 3 Proportion of energy actually available to body: 92.2 In bread alone " 93. 4 a Calculated according to the assumption that 90 per cent of the fat in the bread is digestible. 38 During this experiment the subject eliminated 7,317.4 grams urine, containing 87.08 grams nitrogen. The total nitrogen balance per day was therefore as follows: Income in food, 26.0:* grams; outgo in urine, 21.77 grams, and in feces. 1.1 !> grams, implying a gain of 3.13 grams nitrogen, corresponding to 19.6 grams protein. DIGESTION EXPERIMENT NO. 316. Emdqffood. — Milk, and bread made from straight flour. Subject. — Man No. 2, a> in experiment No. 31<>. Weight. — At the beginning and close of the experiment, 166 pounds. Duration. — Four days, with twelve meals, beginning with breakfast April 28, 19(>2. Table 25. — Result* of digestion experiment No. 316. Sample No. Weight of material. Pmtein. Fat. Carbo- hydrates. Ash. Heat of combus- tion. Food consumed : Bread Grams. 3, 480. 12,730.0 Grams. 264.1 380.6 Grams. 13.2 520. 6 'Grams. 1,902.3 612. 3 17.0 98.0 Calories. 9,082 9.445 244 243 Milk Total Feces ( water free » 644. 7 533.8 2.514.6 115. 18,527 113.0 26.1 11.4 14.8 44.0 12.3 28.0 583 246 Estimated feces from food other than bread Estimated feces from bread 14.7 31.7 618.6 249. 4 519.0 2. 470. 6 1 870.6 87.0 17 944 Estimated digestible nutrients in bread Coefficients of digestibility of total food Per cent. Per cent. 95. 9 94. 4 Per cent. 97.2 Per cent. 98.2 9S.3 Per cent. 75.6 Per cent 96.9 Estimated coefficients of di- gestibility of bread f»98.5 Proportion of energy actually available to body : In total food 92 7 In bread alone a 95. 1 1 a Calculated according to the assumption that 90 per cent of the fat in the bread is digestible. During this experiment the subject eliminated 6,556.6 grams urine, containing 92.45 grams nitrogen. The total nitrogen balance per day was therefore as follows: Income in food, 26.81 grams; outgo in urine, 23.11 grams, and in feces. 1.05 grams, implying a gain of 2.65 grams, nitrogen, corresponding to 16.6 grams protein. DIGESTION EXPERIMENT NO. 317. Kind of food. — Milk, and bread made from straight rlour, Subject. — Man No. 3. as in experiment No. 311. Weight. — At the beginning of the experiment. 151 pounds: at the clo$e, 150.25 pounds. Duration. — Four days, with twelve meals, beginning with breakfast April 28, 1902. 39 Tablb 26. — Results of digestion i vperimeni No Sample No. Welghl material. Protein. Fat. Carbo- hydrates. Ash. combus- tion. 24 J 2 13 Food consumed: Bread Milk Total Grams. 3,380 10,150.0 Grams. 252. 7 803.6 Grams. 12.6 415. 1 Grains. 1,820.8 188.2 drums. 16.8 78.2 Calories. 7 ,;i 556. 2 127. 7 2, 808. 5 94.5 16, 222 ■J 1 7 127.0 32. 2 9. 1 19.4 41*4 9.8 34.1 681 Estimated feces from food other Estimated feces from 23.1 31.6 524. 229. 6 408.3 2,267.1 1,788.7 60.4 15, 541 Estimated digestible nutrients Coefficients of digestibility of Per a nt. Per cent. 94.2 90.9 Per cent. 95.5 Per cent 98. 2 98.2 Per cent. 63.9 Per cent. 95.8 Estimated coefficientsof digest- a 97. 4 Proportion of energy actually available to body: 91.8 a 94. 1 I "Calculated according to the assumption that 90 per cent of the fat in the bread is digestible. During this experiment the subject eliminated 4,747.0 grams urine, containing 65.99 grams nitrogen. The total nitrogen balance per day was therefore as follows: Income in food, 23.22 grams; outgo in urine, 1 *)./)<> grams, and in feces, 1.29 grams, implying a gain of 5.43 grams nitrogen, corresponding to 33.9 grains protein. DIGESTION EXPERIMENT NO. 318. Kind of food. — Milk, and bread made from entire-wheat flour. Subject. — Man No. 1, as in experiment No. 309. Weight. — At the beginning of the experiment. 167.25 pounds; at the close, 168 pounds. Duration. — Four days, with twelve meals, beginning with breakfast May 5, 1902. Table ■Results of digestion experiment Xo. 318. Sample No. Weight of material. Protein. Fat. Carbo- hydrates. Ash. Heat of combus- tion. 251 Food consumed: Bread Milk Grams. 3,700.0 12.000.0 drum*. 360. Grani8. 10.0 162. Grains. 1,913.0 570.0 47.0 87.6 Calories. 9, 952 Total 252 Feces ( water free i Estimated feces froni food other than bread Estimated feces from oread Total amount digested Estimated digestible nutrients in bread 668. 2 502.0 i 2,483.0 51.5 10.8 in 616. 486. 161.5 11.4 150 1 2,321.5 1,762.9 134.6 1.231 17,. Ml 40 Table 27. — Remits of digestion experiment No. 318— Continued. Sample No. Weight of material. Protein. , Pat. Carbo- hydrates. Ash. Seat of combus- tion. Coefficients of digestibility of Percent. Percent. Percent. 92.3 97.0 86. S Per cent. 98.5 92.2 Per cent. 66. 3 Per cent. Estimated coefficients of digest "91.3 Proportion of energy actually available to body: In total food 89 3 a 87 9 I a Calculated according to the assumption that 90 per cent of the Eat in the bread Is digestible. During this experiment the subject eliminated 7,889.1 grams urine, containing 84.41 grams nitrogen. The total nitrogen balance for four days was therefore as follows: Income in food, 27.92 grams; outgo in urine, 21.10 grams, and in feces, 2.06 grams, implying a gain of 1.70 grams nitrogen, corresponding to 29.8 grams protein. DIGESTION EXPERIMENT NO. 319. Kind of food. — Milk, and bread made from entire- wheat Hour. Subject. — Man No. 2, as in experiment No. 310. Weight. — At the beginning and close of the experiment, 107.5 pounds. Duration. — Four days, with twelve meals, beginning with breakfast May 5, 1902. Table 28. — Results of digestion experiment Xo. 319. Sample No. Weight of material. Protein. Fat. Carbo- hydrates. Ash. Heat of combus- tion. 251 258 Food consumed: Bread Milk Total Feces (water free) Grams. 3. 655. 12,380.0 Grams. 304.5 371.4 Grams. 39.5 476.6 Grams. 1, 889. 5 588.0 Grams. 46.4 90.4 Calorics. 9.831 9,100 675. 9 516.1 2, 477. 5 136.8 18, 931 253 302. 63.4 11.1 35.2 23.8 140.1 11.8 63.3 1.332 E-ti mated feces from food other than bread Estimated feces from 351 52. 3 n.4 128. 3 981 Total amount digested Estimated digestible nutrients in bread Coefficients of digestibility of total food "Z": 612. 5 252.2 480. 9 28.1 2. 387. 4 1.761.2 73.5 17, 599 8,850 Per cent. Per cent. 90.6 82.8 Per cent. 93. 2 71.1 Per cent 94.3 93.2 l\r cent, 53.7 Per cent 92.9 Estimated coefficients of di- gestibility of bread 90.0 Proportion of energy actually j available to body: 88.9 86. 8 During this experiment the subject eliminated 6,910.1 grams urine, containing 101.58 grams nitrogen. The total nitrogen balance per day was therefore as follow^: Income in food. 28.21 grams; outgo in urine, 41 25.30 grams, and in feces, 2.57 prams, Implying a gain of 0.25 gram nitrogen, corresponding to 1.6 grains protein. DIGESTION EXPERIMENT NO. 320. Kind <>f food. — Milk, and bread made from entire-wheat Hour. Subject. -Man No. 3, as in experiment No. 31 1. Weight. — At the beginning of the experiment, L50 pounds; at the close, 151.5 pounds. Duration. -Four days, with twelve meal-, beginning with breakfast May 5, 1902. Table 29. — Results of digestion exp* rirru ni No. S20. Sample No. Weight of material. Protein. Fat. Carbo- hydrates. Ash. Seal of combus- tion. 251 258 Food consumed: Bread Milk Grams. 3, 650. 11,750.0 Grams. 304.0 352.5 Grams. 39.4 452. 4 (i rums. 1,887.1 558.1 Grams. 46.3 85.8 Calories. 9,818 Total 656. 5 491.8 2,445.2 132. 1 IS, 454 254 262.0 48.9 10.6 15.7 135. 6 11.2 61.7 1,045 Estimated feces from food other Estimated feces from bread Total amount digested 38.3 124. 4 607.6 265. 7 476.1 2, 309. 6 1.762.7 70J 17,409 Estimated digestible nutrients in bread Coefficients of digestibility of total food P< r a nt. Pi r a ut. 92.5 S7.4 Per cent. 96.8 Per cent. 94.4 93.4 Per <■< nt. 53.3 Per <■< nt. 94.3 Estimated coefficients of di- gestibility of bread "92.7 Proportion of energy actually available to body: In total food 90.2 a 89. 4 a Calculated according to the assumption that 90 per cent of the fat in the bread is digestible. During this experiment the subject eliminated 5,476.6 grams urine, containing 88.17 grams nitrogen. The total nitrogen balance per day was therefore as follows: Income in food, 27.44 grams; outgo in urine. 22.04 grams, and in feces 1.96 grams, implying a gain of 3.44 grams nitrogen, corresponding to 21.5 grams protein. DIGESTION EXPERIMENT NO. 321. Kind .'. — Continued. Sample No. Weigbt Protein, material. Km ' haI - hydrates. Aah. combus- tion. Coefficients of digestibility of total food ." Percent. Per cent. U. Per cent. 90.2 91.6 T.ii l'> r c at. 58. l Estimated coefficients of digest- ibility <>f bread so.l 81.7 Proportion of energy actually available to body: In bread alone During this experiment the subject eliminated 4,532 grams urine, containing 52.57 grams nitrogen. The total nitrogen balance per day was therefore as follows: Income in food, 27.94 grams; outgo in urine. 13.14 grams, and in feces. 2.7t> grams, implying a gain of 12.04 grams nitrogen, corresponding to 75.2 grams protein. DIGESTION EXPERIMENT NO. 323. Kind of food. — Milk, and bread made from graham flour. Subject — Man No. 3, as in experiment No. 311. Weight. — At the beginning of the experiment. 151.25 pounds; at the close, 150.5 pounds. Duration. — Four days, with twelve meals, beginning with breakfast May 16, 1902. Table 32. — Results of digestion experiment No. 828. Sample No. Weight of material. Protein. Fat. Carbo- hydrates. Ash. Heat of combus- tion. 260 259 Food consumed: Bread Milk Total Grams. 3, 580. o 11.000.0 Qrams. 299. :; :>5,. ■"> Grams. 31.1 189.5 Grams. 1,832.9 553. 3 Grams. 51.9 84.7 Calories. 9. 379 8,540 G56. 8 520. 6 2. 3.N5. 2 i3ti. t; 17.92") 26S Feces ( water free | Estimated feces from food other than bread 384.0 73.4 10. 7 31.7 24.5 202. 3 11.1 1,001 348 Estimated feee- bread from 191.2 Total amount digested Estimated digestible nutrients in bread Coefficients of digestibility of total food Estimated coefficients of diges- tibility of bread Proportion of energy actually available to body: In total food In bread alone 583. I 188.9 2.1->3.9 1,041.7 00. 10, 324 8,126 t. Percent. Per cent. Percent. !■ 91.5 91.1 79.0 87.0 83. 5 During this experiment the subject eliminated 4,509 grams urine, containing 85.16 grams nitrogen. The total nitrogen balance per day was therefore as follows: Income in food. 27.42 grams: outo-o in 44 urine, 21.29 grams, and in feces. 2.94 grams, implying a gain of 3.19 grams nitrogen, corresponding to 19.9 grams protein. SUMMARY OF RESULTS OBTAINED WITH SOFT WINTER WHEAT PRODUCTS. In Table 33 a summary is given of the digestibility of the nutrients and availablity of the energy of the entire food of the various digestion experiments with milk and white bread from mixed-grade Hour, white I tread from straight-grade Hour, entire-wheat bread, and graham, aJl ground from soft winter wheat. Table 33, — Summary of digestion experiments with soft winter wheat; digestibility of nutrients and avauabUity of em rgy of total food. Experi- ment No. Subject Kind of food. Protein. Fat. Carbo- hydrates. Energy. 309 310 l 2 3 1 2 3 1 2 3 1 2 3 1 2 3 Experiments with Indiana wheat: Milk and white bread (mixed grade i . . . do Per cent. 95. 8 93.4 90.3 Per <■' at. 93. 7 93. 5 95. * Pi r ''nt. 96.2 96.9 96. 2 /"'/• cent 90.4 90.3 311 ....do 9('.4 93. 2 94.2 90.4 90 4 Milk and entire-wheat bread ....do ....do Average of 3 Experiments with Michigan wheat: Milk and white bread (standard patent i do ....do Average of 3 . . 312 313 314 93. 6 91.6 88.8 97.1 93.8 97.0 92.1 91.7 90. 8 So. 6 ST. 7 87.5 91.3 90.0 91.5 ^7.9 315 316 317 95.2 95.9 94. 2 97.7 97.2 95. 5 97.7 98. 2 98. 2 92.2 92.7 9-1.8 95.1 90.8 98. 92.2 Milk and entire-wheat bread 318 92.3 90.0 92. 5 97.0 93.2 96.8 93. 5 94.3 94. 4 S9.3 319 320 --..do ....do .* Average of 3 90.2 91.8 95.7 94.1 89. 5 Milk and graham bread 321 89.1 89. 7 88.8 95. 5 90.2 93.9 91.1 91.6 91.5 87. 2 322 323 ....do ....do SO. 2 87.0 Average of 3 89.2 93.2 91.4 86.8 The results summarized in the table show that, in general, the ration consisting of milk and white bread made from the patent grade flour was more digestible than the rations of milk and bread made from either of the other kinds of flour, also that a larger percentage of energy was available to the body in the case of white bread and milk than from the entire-wheat or graham bread and milk. In the experiments with Indiana soft wheat individual differences a^ regards the ability to digest the bread and milk rations were quite pronounced with the various subjects; in the ease of the white bread, a difference of about 5.5 per cent in the digestibility of the protein being- observed. Subject No. 1 digested the wheat bread and also the entire- wheat bread more completely than did subject No. 2 or 2s o. 3. With 45 each subject, however, the digestibility of the ration with white bread was greater than that with entire wheat. In the experiments with Michigan soft wheat individual differences are noticeable, but they arc less pronounced, and, as was the case with the other wheats, each subject digested the ration of white bread and milk more completely than bread made from either of the other flours. In Table 34 the calculated digestibility of the nutrients and availa- bility of the energy of the bread alone are given: Table .'54. — Summary of di,i experiment* with soft winter wheat; digestibility of nutrients end availability of energy of bread (done. Experi- ment No. Subject 309 l 310 2 311 3 312 1 313 2 314 3 315 1 310 2 317 3 318 1 319 ■1 320 3 1 321 1 322 2 323 3 Kind of food. Experiments with Indiana wheat: White bread (mixed grade noun ....do ....do Average of 3.. Entire-wheat bread ....do ....do Average of 3. Experiments with Miehigan wheat: White bread (standard patent). do ....do Average of 3.. En tire- wheat bread ....do ....do.../ Average of 3. Graham bread. ....do ....do Average of 3. **>**»■ b$$eV **»•* 1>, r n nt. 94.2 89.4 83.0 I'll- VI lit. I'n- CI lit. 95.6 90.4 96.6 ' 90.4 95.8 i 90.4 88.9 96.0 ; 90.4 89.5 84.9 79.3 90.3 v.*. 8 ■ 88. 8 85. 2 84. 5 82.9 84.6 89.6 84.2 93.0 94.4 90.9 97.6 98.3 98, -1 93.4 95.1 94.1 92.8 98. 94.2 86.8 82.8 87.4 92. 2 93. 2 93.4 s:. 9 86.8 89.4 85.7 92.9 88.0 79.2 80.1 79.0 88.9 89.5 1 89.6 : 82. 7 81.7 S 82. 6 These results are calculated, as explained on page 1H. by assuming that 97 per cent of the protein and 98 per cent of the carbohydrates of the milk were digested." The average result of the experiments with flour milled from Indi- ana soft winter wheat shows that S8.9 per cent of the protein and :♦♦; per cent of the carbohydrates of the white bread from mixed-grade flour were digested, and that 90.4- per cent of the energy was available. As regards the bread from entire-wheat flour, ground from the same lot of wheat, S±.t) per cent of the protein and 89.6 per cent of the car- alt was also assumed that 95 per cent of the fat of the milk would be. digested, but with this factor the digestibility of the fat of bread could be computed satisfactorily in only a few cases; therefore figures for this constituent are left out of Table 34. In all cases where the digestibility of bread fat could not be computed it was assumed, in order to estimate the available energy of the bread, that 90 per cent would be digested. 46 bohydrates were found to be digestible, and 84.2 per cent of the energy to be available. It will be observed, further, that with each of the sub- jects the nutrients of the white bread were more digestible and the energy more available than was the case with the entire- wheat bread. The white bread made from straight-grade flour milled from Michi- gan soft winter wheat had the highest digestibility of any of the sam- ples ground from this variety, namely. 92.8 per cent of the protein and 98 per cent of the carbohydrates, while 94.2 per cent of the energy was available to the body. Of the protein of bread from the entire- wheat flour milled from the same lot of wheat. 85.7 per cent, and of the carbohydrates 92.9 per cent were digestible. 88 per cent of the energy being available to the body. The lowest coefficients of digesti- bility were found in the graham bread, the values being 79.4 per cent for the protein. 89.3 per cent for the carbohydrates, and 82.6 per cent for the energy available to the body. As will be seen, there was a dif- ference of 13.4 per cent in the average digestibility of the protein of the graham bread and white bread made of flour from the same lot of wheat, while 8.7 per cent less of the carbohydrates of the graham bread was digestible, and 11.6 per cent less of the energy was avail- able. As in the case of the entire ration, differences attributable to individuality are noticeable, which are, however, not great enough to invalidate the general deduction that white bread is the most digesti- ble, graham bread the least, and entire-wheat bread intermediate between them. Table 35 gives a summary of the experiments on the basis of the pro- portion of total and digestible nutrients and available energy in the different grades of flour as milled from soft winter wheat: Table 35. — Proportion of total and digestible nutrients and available energy in different grades of soft winter-wheat flour as milled. Num- ber of sample. Grade of flour. 221 Mixed-srrade flour . . 219 Entire-wheat flour . 24Q Straight white flour 211 Entire-whea; 242 Graham flour Protein. Gar bohydrates. Total Digest- T , Digest- lotaL ible. lotal - ible. Per cent. Per cent. Per cent. 12. 30 10.93 75.91 12.80 10. -2 71.10 10.92 10.13 77. 15 12. 01 10. 29 74.17 12. 21 9.72 73. 27 Per cent. 72.90 00.66 75. 61 S - 65. 43 Heat of combus- tion per gram. Total. Avail- able. Calories. 4.010 4. 020 3.799 3.906 Calories. 3.645 3.384 3. 579 3. 399 3. 226 The digestible nutrients were obtained by multiplying the percent- age of the total nutrients by the average digestion coefficients given in Table 34. The mixed-grade flour, for example, contained 12.3 per cent total protein, which was found to be 88. 9 per cent digestible, being therefore equivalent to 10.93 per cent of digestible protein. The mixed-grade flour prepared from the Indiana wheat contained 10.93 per cent digestible protein, 72.90 per cent digestible carbo- 47 hydrates, and 1 gram of the Hour yielded 3.645 calories of available energy. The entire-wheat flour prepared from the same wheal yielded 10.82 per cent digestible 'protein. 66.87 per cent digestible carbo- hydrates, and 3.375 available calories per gram. The difference in digestible protein is small, being 0.11 percent in favor of the mixed- grade flour. The difference in the digestible carbohydrates Is quite large, being 6.24 per cent in favor of the mixed-grade flour. The difference in the available energy is also large, amounting to 0.26] caloric per gram in favor of the white Hour. While there ts no material difference as to the amount of digestible protein in the two kinds of Hour, the differences in digestible carbo- hydrates and available energy are decidedly in favor of the mixed-grade flour. The entire-wheat flour contained a larger amount of protein. but, as shown in Table 34, this protein is less digestible than that of the mixed-grade flour, which was more finely granulated. The straight-grade flour prepared from the Michigan wheat con- tained 10.13 per cent digestible protein, 75.61 per cent digestible carbohydrates, and 3.574 calories of available energy per gram. Com- pared with graham flour, this shows 0A per cent of digestible protein, 10.18 per cent of digestible carbohydrates, and 0.353 calorie of avail- able energy per gram in favor of the white flour. Compared with the entire-wheat flour, the results show a difference of 6.81 per cent digestible carbohydrates and 0.180 available energy per gram in favor of the straight-grade flour; the difference in digestible protein, though too small to be of significance, is 0.16 per cent in favor of the entire- wheat flour. In the description of the samples it was stated that the straight-grade flour did not contain all of the granular middlings which are usually included in the preparation of ordinary straight flours. Had the flour contained the granular middlings, the percent- age of protein, it seems fair to conclude, would have been higher than 10.92. While the difference in total protein is 1.1 per cent in favor of the entire-wheat flour, the higher degree of digestibility of this con- stituent in the straight-grade flour makes the figures for the total digestible protein in the two kinds of flour practically the same. Hence, what is gained from the somewhat larger amount of protein in the entire-wheat and graham flours is lost in digestibility. While the difference between the digestible protein in the straight-grade and entire-wheat flours prepared from the same lot of soft wheat is small, the difference in digestible carbohydrates is large, being 6.8 per cent in favor of the white flour. Since a larger amount of digestible carbo- hydrates and available energy is secured from the mixed and straight- grade flours than from the entire-wheat flour and no appreciable differences were observed as to digestible protein, it would appear that a larger total amount of nutrients and energy is available to the 48 body from the straight than from the entire-wheat or graham flours, a conclusion in accord with the results of all our former work. That the lower degree of digestibility of the entire-wheat and graham flours was probably due at least in part to a coarser granulation of the particles, which consequently exposed a relatively smaller amount of surface to the action of the digestive fluids, was shown by a microscopical examination of the feces. The feces from both the entire-wheat and the graham flours under the microscope showed a larger proportion of starch particles that had not been acted upon in the digestive tract than the feces from standard patent flour. The micro-photographs reproduced (Pis. I— III) show the fineness of division of the three sorts of flour and the starch granules in the feces obtained from the standard patent, the entire-wheat, and the graham flours, prepared by grinding in a mortar. These deductions are in accord with the results of numerous micro- scopical studies of the feces from different sorts of wheat products, and in this connection it is interesting to refer to some of these and closely related investigations. Among others may be mentioned the work of Runner/' Pappenheim/ Constantinidi, * and Raudnitz. d In general it may be said that these investigators found that starch was very thoroughly digested, but that the cells making up the outer portion of the wheat berry were little attacked by the digestive juices, and hence the contents of such cells were not assimilated. Rubner pointed out that the amount of undigested nitrogen increased with an increase in the amount of the outer portion of the grain retained in flour in milling. Rathay^ reports experimental studies, of which he himself was the subject, in which the diet for a week consisted of graham bread and tea. The bread was made without leaven or yeast. The feces from the fifth and seventh day were examined microscop- ically. He found that the grain portions which had been little masti- cated were softened, but almost entirely undigested. From only a few of the outer cells of the endosperm had the starch grains and the proteid materials disappeared, while the greater part of these nutri- ents was excreted unchanged. The general conclusion from his inves- tigations was that the greater portion of the feces consisted of undi- gested residues of wheat bran in the form of large flakes composed of the seed coats and aleurone layer. The latter leaves the intestines unchanged, probably because the thick walls of the aleurone cells pre- vent the action of digestive juices upon the cell contents. So far as can be learned, this investigation was the first which at all satisfac- _ — i , _ _ — — — — "Zt^chr. Biol., 15 (1879), p. 115. i' Lehrbucfa der Mi'illerei (1890), 3d ed., cited by Moeller. ^Ztschr. Biol., 23 (1887). p. 447. often claimed that the larger proportion of mineral matter, and especially phosphorous compounds, in whole-wheat and graham flours is a reason for preferring them to patent flour. In this case also it is undoubtedly true that the proportion of mineral con- stituents which is digestible, or. in other words, which the body can retain, from the different sorts of flour, must be considered, as well as the amounts which chemical analysis shows to be present in the food. In view of the fact that there is apparently no satisfac- tory method for determining the proportion of ash in the feces, derived from metabolic products, and that it is, therefore, impossible by present methods to determine the true digestibility of the mineral constituents, no values for the digestibility of ash have been included in the present bulletin. It may be noted in this connection that it is a well- recognized fact that when the coarser milling products are fed to cattle no great amount of phosphorus (one of the most important manurial elements) is retained in the animal body. This may possibly be an indication that the phosphorus, even if present in con- siderable amounts in the feed, is not in a form which can be assimilated by animals. This is, however, little more than conjecture, and more experiments with man and the lower animals are needed before satis- factory conclusions can be drawn. Briefly stated, the most important deductions from the results of these investigations with hard and soft wheat are in accord with the conclusions drawn from the earlier investigations of this series. The nutritive value of flour, in so far as the quantities of digestible protein, fats, and carbohydrates, and available energy are concerned, is not increased by milling the wheat in such a way as to retain a large pro- portion of bran and germ. The differences in the amounts of total nutrients furnished the body by the various grades of flour are, how- ever, relatively small, all grades being quite thoroughly digested. The coarser flours have a tendency to increase peristaltic action, and are on this account especially valuable for some persons. Judged by 52 composition and digestibility, all the flours arc very nutritious foods, which experience has shown are wholesome as well. When also the fact is taken into account that they furnish nutritive material in an economical form, their importance is evident. The fact must not be lost sight of that using different grades of flour for bread making and other household purposes offers B convenient method of adding to the variety of the daily diet, a matter which is of undoubted importance. LIST OF PUBLICATIONS OF THE OFFICE OF EXPERIMENT STATIONS ON THE FOOD AND NUTRITION OF MAN- Cdntitiued, Hul. 75. Dietarj Studies of University Hunt Crews* Hy u. < >. Atwater and A. P. Bryant. Pp. 72. Price, 5 Ants. Hul. M. Nutrition Investigations at the California Agricultural Experiment Station, ISM L89f M. E. Jaffa. Pp. 89. Price, 5 cent-. Hul. 35. A Report of Investigations on the Digestibility and Nutritive Value of Bread. Bj < i> Woods and L. H. Merrill. Pp. 51. Price, r > cents. Hul. 89. Experiments on the Effect ol Muscular Work apon tin- Digestibility of Pood and tip- Metab oiisui of Nitrogen. Conducted at the Universit} of Tennessee, i v, .'T L899. Bj C. E. Wait Pp. 77. Trice. 5 cents. Hul. 91. Nutrition investigations at. the University of Illinois, North Dakota Agricultural College, and Lake Brie College, Ohio, 1895-1900. Hy H. s. < Irindley mid .1. L. Sajnmis, B. P. Ladd, and Isabel Hevierand Elizabeth C sprague. Pp. 12. Price, 5 cents. Hul. 98, The Effect of Severe and Prolonged Muscular Work on Food Consumption, Digestion, and Metabolism, hy W. O. At water and II C. Sherman, and the Mechanical Work and Efficiency of Bicyclers, by R. C. Carpenter. Pp. 67 Price. 5 cents. Bui. 101. studies on Bread and Bread Making at the University of Minnesota in 1899 and 1300. By Harry Snyder. Pp. 66. Price, 5 cents. Bid. 102. Experiments on Losses In Cooking Meat, 1898-1900. By H. S. Grihdley, with the coopera- tion of H. McCormack and H. C. Porter. Pp. 64. Price. 6 cent-. Bui. H>7. Nutrition Investigations Among Fruitarians and Chinese at the California Agricultural Experiment Station. 1899-1991. By M. K. Jaffa. Pp. 43. Price. 5 cents. Bnl. loo. Experiments on the Metabolism of Matter and Energy in the Human Body. 1*98-1900. By W. O. Atwater and F. G. Benedict, with the cooperation of A. P. Bryant, A. W. Smith, and J. F. Snell. Pp. 147. Price, 10 cents. Bui. lit - .. Dietary Studies in New York City in 1X% and 1S;»7. Hy W. 0. Atwater and A. P. Bryant. Pp. 83. Price, •"> cents. Bui. 117. Experiments on the Effect of Muscular Work upon the Digestibility of Food and the Metab- olism of Nitrogen. Conducted at the University of Tennessee, 1899-1900. By C. E. Wait. Pp. 43. Price, 5 cents. Bui. 121. Experiments on the Metabolism of Nitrogen, Sulphur, and Phosphorus in the Human Organism. By H. C. Sherman. Pp. 47. FARMERS' BULLETINS. *Bul. 23. Foods: Nutritive Value and Cost. By W. Q. Atwater. Pp. 32. Bui. 34. Meats: Composition and Cooking. By C. D. Woods. Pp. 29. Bui. 74. Milk as Food. Pp. 39. Bui. 86. Fish as Food. By C. F-. Lang-worthy. Pp.30. Bui. 93. Sugar as Food. By Mary H. Abel. Pp. 27. Bui. 112. Bread and the Principles of Bread Making. By Helen W. Atwater. Pp. 39. Bui. 121. Beans, Peas; and other Legumes as Food. By Mary H. Abel. Pp 32. Bui. 128. Eggs and their Uses as Food. Hy C. F. Langworthy. Pp. 32. Bui. 142. Principles of Nutrition and Nutritive Value of Food. By W. O. Atwater. Pp. 48. CIRClLAR. ( ir. 16. The Functions and Uses of Food. By C. F. Langworthy. Pp. 10. SEPARATES. *Food and Diet. By W. O. Atwater. Reprinted from Yearbook of Department of Agriculture for 1894. Pp. 44. Some Results of Dietary Studies in the United States. By A. P. Bryant. Reprinted from Yearbook of Department of Agriculture for 1898. Pp. 14. Development of the Nutrition Investigations of ihe Department of Agriculture. By A. C. True and R. D. Milner. Reprinted from Yearbook of Department of Agriculture for 1899. Pp. 16. The Value of Potatoes as Food. By C. F. Langworthy. Reprinted from Yearbook of Department of Agriculture for 1900. Pp. 16. 1 Dietaries in Public Institutions. By W. 0. Atwater. Reprinted from Yearbook of Department of Agriculture for 189L Pp. 18. Scope and Results of the Nutrition Investigations of the Office of Experiment Stations. Reprinted from Annual Report of the Office of Experiment Stations for the year ended June 30, 1901. Pp. 50. ^ii&affiSK ^R siT L.?mnr\\rt\\\\\\\\l\\ ] wmsm 3 l* D