TX 556 .5 .C5 Copy 1 T9. ' I ill. ■M C><^^--^ ■c c^8fes~ Jn [Reprinted from American Chemical Journal, Vol, VI, No. 5.] Contributions from the Sheffield Laboratory of Yale College. XXL— ON THE RELATIVE DIGESTIBILITY OF FISH FLESH IN GASTRIC JUICE. By R. H. CHiTTENDErj AND Geo. W. Cummins. The value of food as nutriment depends primarily upon the presence in suitable quantity of elements, or combination of ele- ments, capable of supplying the needs of the body ; coupled with this, however, is the ease with which the food stuff in question can be rendered available by the system for its wants. This, or in other words its digestibility, constitutes a very important item in determining the true nutritive value of any food. If, of two foods possessing a like chemical composition, one be more easily diges- tible, that one, though containing no more available nutriment than the other, is in virtue of its easier digestibility more valuable as a food stuff and in one sense more nutritious, as well as more economical for the system. Both chemists and physiologists have appreciated the impor- tance of all data relative to the nutritive value of foods. But hitherto nearly all work in this direction has been confined to a study of chemical composition, and only occasionally to digesti- bihty. The mere fact, however, that a substance contains a certain percentage of nitrogen is not alone sufficient. We need to know in addition, not only how much of the nitrogen passes through the body unabsorbed, thus indicating how much is ordinarily available for nutriment, but we need to know likewise how long the food stuff remains in the stomach, how quickly it is acted upon by the digestive juices, and, finally, how much passes out undigested ; points of great importance to the healthy system, but still more so to the system weakened by disease. There are two ways of determining the digestibility of a food stuff in gastric juice. One consists in the introduction of a weighed amount of the substance into the stomach of a man or animal through a fistulous opening, and noting the length of time required for its solution; the other, in the use of an artificial gastric juice by which the amount of substance capable of being dissolved and digested in a given time can be quantitatively ascertained. 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Average results from each sample of cooked flesh. Beef Beef Beef Veal Veal Mutton Lamb Spring chicken (light meat) " (dark meat) Lake White (Coregonus clupeiformis] Shad (Clupea sapidissima) " " (light meat " " (dark meat) Salmon (Salmo salar) Tautog (Hiatula onitis) Porgee (Sparus chrysops) Blue fish (Pomatomus saltator) Mackerel (Scomber scombrus) Halibut (Hippoglossus vulgaris) Flounder (Paralichthys dentatus) Sea Bass (Serranus atrarius) , Pike (Esox lucius) Haddock (Gadus aeglifinus) Herring (Clupea harengus) , Striped Bass (Roccus lineatus) Red Snapper (Lutjanus Blackfordi).., Trout, brook (Salvelinus fontinalis).. Sea Robin (Prionotus palmipes) , White Perch (Roccus Aniericanus)... Fresh Cod (Gadus callarias) , Weak fish (Cynoscion regale) Yellow fish(Perca Americana) Eel (Anguilla rostrata) Window Pane (Bothus maculatus) ... Flat fish (Pleuronectidae Americanus Lobster (young) " (large female) " (large male) Crab Frogs' legs 19 5.024 5.206 5-138 4.992 4.858 6.168 5-974 5-32S 5-340 5.112 6.266 6.076 6.526 6.212 6.300 4.120 4-512 3.968 3.892 5.102 4.056 4.608 4-234 3.926 3.648 4.89S 4.164 4.418 3.916 4-374 3-93^ 3.658 3-956 3.624 4-356 3-674 3-430 4-350 4.258 4.152 4.714 3-572 4.1607^ 4-1167 \ 3.S6ioJ 4.1742 ) 3.5052) 3-7287 3-5580 3-5090 3.4160 3-8350 3-6455 3-9352 3 5332 3-7345 3-6335 3.5660 3-5215 3-5885 2.9717 3-4895 3.4600 3-4525 3-3995 3-3582 3-3382 3-3317 3.2770 3-3040 3-1745 3-1572 2-9515 2.9292 2.9180 2.9037 2.9062 2.8927 2.7065 3-5532 3.1990 2.7960 2.7165 3-2535 i e i ^ o o J? ^ '^ ^ o -^ — J) ii-^ «^^ S Z=IOD.OO = 94.89 92.15 87-93 86.72 84.42 94.78 90.09 97.25 87-32 92.29 89.80 88.13 87.03 88. 69 73-44 86.24 85-51 85-32 84.01 82.99 82.50 82.34 80.99 81.65 78.45 78.03 72.94 72-39 72.1 1 71.76 71.82 71.49 66.89 87.81 79.06 69.13 67-13 80.46 13 cerned, there was no appreciable difference in the three samples. Bearing in mind, however, these possible variations, it is very evident from our results that the average digestibility of fish flesh is far below that of beef similarly cooked. In but two instances, in the case of shad and lake white, does the digestibility of fish flesh approach that of beef, although, from the average of our experi- ments, several are as easily digestible as mutton, lamb and chicken. Pavy' states that fish with white flesh, such as the whiting, etc., are less stimulating and lighter to the stomach, or more easy of digestion, than fish with more or less red flesh, as the salmon. Our experiments confirm this statement so far as digestibility is con- cerned. Thus the average digestibility of the salmon and trout is considerably below the average of the more digestible white fish. The difference between the digestibility of the light and dark meat of the same fish is somewhat striking, as in the case of the shad, where the digestibility of the former was found to be 97.25, as compared with beef, while the dark flesh was 87.32. A similar difference, though very much smaller, is to be noticed between the light and dark meat of the chicken. This difference in digestibility is in part due, without doubt, to the amount of fat present, for, as Pavy states, in the flesh of white fish there is but little fat, it being accumulated mainly in the liver of the animal, while in red fish there is more or less fatty matter incorporated with the muscular fibres. For a similar reason eels, mackerel and herring are, according to Pavy, less suited to a deli- cate stomach than some of the white fish, and our experiments show that in digestibility two of them stand below the more diges- tible white fish ; mackerel, however, from our single experiment with the white portion of the flesh, showed a comparatively high digestibility. In all of our experiments, however, with white fish, we rejected the outer layer of dark flesh, except in the case of the shad. The varying differences in digestibility are not to be considered as due wholly to differences in the amount of fat in the flesh ; thus the flesh of fresh cod contains but litde fat, and yet it is one of the most indigestible of the white fish experimented with. This agrees with Pavy V experience " that it is a more trying article of food to the stomach than is generally credited." Again Pavy^ makes the fol- lowing statement, based on his experience in fish dietetics, " of all fish, the whiting may be regarded as the most delicate, tender and 1 On food and dietetics. Amer. ed., 1874, p. 171. ^ Loc czt.p. 173. ^Loc. cit. p. 172. H easy of digestion." " The haddock is somewhat closely allied, but is inferior in digestibility," while " the flounder is light and easy of digestion, but insipid." With all these statements our results agree perfectly, assuming the lake white of our experiments to be analo- gous to the English whiting. Maly,' in speaking of the digestive processes in the living stom- ach, says that raw flesh is more slowly digested than cooked, probably for the reason that with dilute acids the coagulated albumin of cooked flesh is more easily converted into acid albumin. Likewise, that the flesh of young animals is more rapidly digested than that of older, while fat flesh is but slowly attacked, as the melted fat surrounds the muscle fibres. With reference to the first of these statements, Jessen ^ found, by experimenting with per- fectly lean beef of known age, that he had only a small undigested residue in an artificial digestion of the raw beef, but with the same amount of partially boiled beef a much larger amount remained undigested, and when thoroughly boiled a still larger residue was found. Taking the amount of undigested residue as a measure of the digestibility, the proportion with the same sample of beef was as follows: raw beef lOO, partially boiled 167, thoroughly boiled 317. The gastric juice employed by Jessen, however, could hardly be considered as made up of a dilute acid, containing, as it did, 2.5 and 5.0 per cent, of concentrated hydrochloric acid. In our own experiments, with a gastric juice containing but 0.2 per cent, of pure hydrochloric acid, positive results were obtained as follows : isi sample of Beef. zd sample of Beef Raw. Cooked (steamed). Raw. Cooked (steamed). Amount digested from 20 grams. 4.0792 3.8610 4-3785 4.1607 Relative proportion. 1 00.0 94-65 lOO.O 95-04 The difference here, then, is not so great, though sufficiently pro- nounced to indicate plainly the influence of cooking. A similar experiment with a sample of blue fish gave a like result : Amount digested from 20 grams. Relative proportion, ' Hermann's Handbuch der Physiologic 5, iii. ' Zeitschrift fiir Biologic 19, 128 Raw. Cooked (steamed), 3.7617 3-5885 1 00.0 95-39 15 With the raw beef, however, digestion was so near complete that a second experiment was tried with a larger quantity, as fol- lows : From 20 grams. From 30 grams. Amount digested (raw beef), 4-3785 5-76 lo Relative proportion, loo.o 131 -57 This would make the relativedigestibility of cooked (steamed) and raw beef as loo.o : 142.38, a difference nearly as great as that found by Jessen between raw and partially boiled beef. It is plain, then, that the digestibility of raw beef is considerably greater than cooked. Whether the relative digestibility of raw and cooked fish, given above, would be changed by increasing the amount of flesh added, we cannot say. It is a point of little importance, but from the fol- lowing experiment with cooked fish it probably would make but little difference. This experiment with cooked sea bass was tried mainly to ascertain the quantity of flesh best adapted to 200 cc. of our standard gastric juice : From 20 grams. From 30 grams. From 40 grams. Amount digested, 3-3995 3-2325 2.5200 Relative proportion, loo.o 95.08 74-12 In this case, increasing the amount of material plainly diminishes the digestive action. With regard to the second statement of Maly's, above quoted, our experiments tend to show that, in some instances at least, the flesh of younger animals is less easily digestible than that of older animals of the same species. This is well illustrated in the greater digestibility of mutton as compared with lamb. 'Tfn'.^i i w iii x^. /^ LIBRARY OF CONGRESS 014 487 271 A