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 MNliVERSlTYOFtLUNOjS, 
 
Agricultural Experiment Station, 
 
 BULLETIN NO. 91. 
 
 PREVENTING CONTAMINATION OF MILK. 
 
 BY WILDER J. FRASER. 
 
 URBANA, ILLINOIS, DECEMBER, 1903. 
 
SUMMARY OF BULLETIN No. 91. 
 
 INTRODUCTION. Investigation has shown that all of the troublesome changes 
 that take place in milk and make it such a difficult product to handle properly are 
 caused by bacteria. Page 221. 
 
 BACTERIA. Bacteria are single-celled plants, so minute that several hundred of 
 them placed closely side by side would equal only the thickness of ordinary writing 
 paper. Page 221. 
 
 SOURCES OF BACTERIA IN MILK. Bacteria exist in immense numbers in the 
 air, and in dust and dirt of every description, and for this reason it is difficult indeed 
 to secure milk free from germs. Page 222. 
 
 THE EFFECT OF BACTERIA ON MILK. Bacteria not only cause milk to sour in 
 a short time, but they make it less wholesome, and often impart a bad flavor. 
 
 Page 223. 
 
 OBJECT OF THE INVESTIGATION. The purpose of the investigation reported in 
 this Bulletin was to determine the effect of the different common operations per- 
 formed each day in dairies and dairy barns upon the bacterial content of milk, and 
 to find the most practical methods by which this contamination could be reduced 
 to the least possible amount. Page 224. 
 
 METHOD USED. Petri dishes filled with a sterile nutrient medium were exposed 
 for a definite length of time, and then held at a warm temperature for three days, 
 when the colonies were counted. The basis taken was the number of colonies 
 developed on 63 square centimeters of surface from a half-minute exposure. 
 
 Page 224. 
 
 CHECKS ON THE WORK. To learn whether petri dishes might become con- 
 taminated before or after direct exposure, dishes were left in dusty places in the 
 barn, but not exposed. In the thirty-nine dishes thus treated, but seven colonies 
 developed. Page 227. 
 
 BACTERIAL CONDITION OF OUTDOOR AIR. Of the exposures made in the open 
 field, fifty percent were sterile, while of those made in the barnyard, twelve percent 
 were sterile. Page 228. 
 
 BACTERIAL CONDITION OF AIR IN DAIRY BARNS. The results obtained in 
 these barns show that with a dry and dusty floor the bacterial content of the air is 
 large when the cows are in the barn, even though they are not brushed and no hay 
 or bedding is moved. With an efficient system of ventilation and a clean cement 
 floor, the number of bacteria in the air is decreased greatly. Dust arising from 
 brushing cows is more heavily laden with bacteria than dust from most other 
 sources. Page 229. 
 
 EXPERIMENTAL MILKING ROOM. The dust which arises from brushing cows, 
 although heavily laden with bacteria, soon settles when the room remains closed, 
 and in half an hour the air is practically free from bacteria. Page 235. 
 
 BOTTLING ROOM. Everything in this room is kept clean, and the floor is 
 usually damp. Eighty percent of the exposures made there were sterile. Page 236. 
 
 WASHING UDDERS BEFORE MILKING. The number of colonies developed from 
 exposures under apparently clean unwashed udders was three times as many as 
 under the same udders after washing. With soiled or muddy udders, such as are 
 frequently found in dairies, the benefits derived from washing udders are much 
 greater than these results show. Page 237. 
 
 WEIGHT OF DIRT WHICH FALLS INTO MILK DURING MILKING. With udders 
 that were apparently clean it was found that an average of 3 times as much dirt fell 
 from the unwashed udders as from the same udders after they were washed. With 
 soiled udders the average was 18, and with muddy udders 90 times as much dirt 
 from the unwashed as from the washed. Page 243. 
 
 CONCLUSIONS. The results of the work described in this Bulletin are of vital 
 importance to the practical dairyman, as they show that extreme cleanliness is 
 absolutely essential to the most successful dairying. Page 245. 
 
PREVENTING CONTAMINATION OF MILK. 
 
 BY WILBER J. FRASER, CHIEF IN DAIRY HUSBANDRY. 
 
 INTRODUCTION. 
 
 It has long been known that extreme cleanliness is absolutely essen- 
 tial to the most successful dairying, but the real reason for this was not 
 known until within the last few decades. Investigations of recent years 
 have shown that all of the troublesome changes that take place in milk 
 and make it such a difficult product to handle properly are caused by 
 bacteria. In fact, successful dairying depends largely upon the ability 
 to limit the number of bacteria obtaining access to milk, and to control 
 those that cannot be kept out. 
 
 Milk becomes contaminated in so many ways in the process of milking 
 that it is extremely difficult to secure it free from germs, but this has 
 been done in an experimental way a sufficient number of times to prove 
 that milk as formed in the milk glands of a healthy cow is germ free. 
 Since bacteria invade the udder to some extent, and develop there, milk 
 as drawn from the udder is not entirely free from germs ; this is especially 
 true of the first milk drawn. 
 
 When milk is secured free from germs, the common phenomenon of 
 souring does not take place, but it remains sweet and practically 
 unchanged indefinitely. It is, therefore, of the utmost importance not 
 only to the milk producer and the consumer, but to the butter and 
 cheese maker as well, that this ideal condition be as nearly reached as 
 possible. By observing a few precautions dairymen can prevent the 
 contamination of milk to a large extent, and thus produce, at but slight 
 trouble or expense, a much better and more valuable as well as a longer 
 keeping product. 
 
 BACTERIA. 
 
 Comparatively little was known of bacteria until within the last two 
 decades, but during this time much attention has been given to the study 
 of these microscopic plants, and the knowledge of them has made won-, 
 derful progress. The study had not advanced far when it was discovered 
 that certain species of bacteria had the power to produce disease, and the 
 reputation which they thus gained clings to all bacteria in the popular 
 mind to-day. With many people the words "bacteria" and "disease" 
 are nearly synonymous terms, although the power to produce disease 
 belongs to a small percentage only of the numerous species of these 
 organisms. Bacteria are the chief agents in decay, and without decay 
 all organic matter would remain unchanged after death. 
 
 221 
 
222 BULLETIN No. 91. [December, 
 
 SIZE. 
 
 These organisms, which are of such great importance, are so extremely 
 minute that it is difficult to gain an adequate conception of their size. 
 If they could be placed closely side by side, it would take several hundred 
 to equal the thickness of ordinary writing paper. Of course, they can 
 be seen only with the most powerful microscope. If bacteria could be 
 magnified to the size of base-balls, a man enlarged in the same propor- 
 tion' would be over fifty miles high. 
 
 FORM. 
 
 In the more complex species of plants and animals, each has a form 
 peculiar to itself. In bacteria, which are single-celled plants, there can 
 be little difference in the form of the different species because of their 
 simple structure and minute size. Although there are hundreds of 
 species of bacteria, they all come under three different forms, which may 
 be represented by balls, rods, and corkscrews. 
 
 [ SOURCES OF BACTERIA IN MILK. 
 
 Since milk, as formed in the milk glands of a healthy cow, is germ 
 free, we would not expect to find bacteria always present in it, at least in 
 such large numbers as usually exist. Freshly drawn milk may contain 
 from 200 to 100,000 bacteria per c. c., or from 800 to 400,000 per tea- 
 spoonful, according to the care with which it is handled. By the time 
 milking is completed, under ordinary conditions, the milk is badly con- 
 taminated indeed. It is then of the greatest importance to the dairy 
 interests to learn the sources of bacteria which gain access to milk. 
 The number found in freshly drawn milk is a good indication of the 
 sanitary conditions under which it was produced. 
 
 Let us pause for a moment and see where these bacteria are in nature, 
 and how they so readily gain access to milk. Investigation has shown 
 that their presence is well-nigh universal. They are found floating on 
 the dust in the air, and in the soil and water. It is difficult to find a 
 cubic yard of air that does not contain thousands of them, and soil and 
 water contain them in vastly larger numbers. In the air of enclosed 
 spaces, as in dwellings and barns, they are much more numerous than 
 out of doors. In the air of barns they are generally abundant, especially 
 if a dust has been raised. They are also found in immense numbers in 
 dung and dirt of every description, on the cows' udders, the hands of the 
 milkers, and not jonly in the seams and cracks of unsterilized dairy 
 utensils, but also clinging to the entire surface. Wherever there is a 
 lodging place for dust, there bacteria will be found in vast numbers. 
 The least stir in the bedding or of the dust on the floor will send myriads 
 of them floating into the air. Everywhere in nature, then, these organ- 
 
1903.] PREVENTING CONTAMINATION OF MILK. 223 
 
 isms exist with the power to multiply with astonishing rapidity unless 
 held in check by the conditions surrounding them. In most places they 
 are dormant or growing very slowly. The bacteria clinging to the hair 
 and dirt on a cow and those riding on the dust in the air, multiply slowly, 
 if at all, but they have the power of growth, and as soon as they find 
 moisture and nourishment, they develop rapidly if the temperature is 
 favorable. 
 
 Freshly drawn milk is especially adapted to the growth of nearly all 
 species of bacteria, as it contains all the elements necessary for their 
 development, and besides affords a favorable temperature. Those that 
 gain access to it, therefore not only contaminate it themselves, but 
 multiply at an astonishing rate if the milk is not immediately cooled to 
 near the freezing-point. The increase of bacteria usually occurs by the 
 simple division of one individual into two. The exceptional power of 
 rapid multiplication is one of their most important properties, especially 
 in relation to dairying. In some species one germ may become two, 
 under favorable conditions, in half an hour. Such multiplication in a 
 geometrical ratio results in an increase of numbers with almost incon- 
 ceivable rapidity. At this rate, starting with 1 organism, in half an 
 hour there would be 2; in one hour each of these would have again 
 divided, making 4; in one and a half hours 8, in two hours 16, in three 
 hours 64, in four hours 256, etc., and if this rate of multiplication could 
 be maintained for twenty-four hours there would be some 17,000,000, 
 all the offspring of a single bacterium within a single day. Fortunately 
 for humanity this maximum multiplication rarely occurs, as various 
 factors soon interpose to check the development of these germs. 
 
 Temperature, moisture, and food supply are the conditions controlling 
 the multiplication of bacteria. Milk at all temperatures furnishes ideal 
 conditions as to moisture and food, and when freshly drawn its tem- 
 perature is ideal for most species. This being the case, all germs that 
 gain access to milk may multiply rapidly unless checked by an arti- 
 ficially low temperature or by the addition of some substance that pre- 
 vents growth. 
 
 The temperature at which bacteria multiply most rapidly varies with 
 the species. Some grow best at 75 F., and others at 90, while a few 
 reach their maximum rate of development at still higher temperatures. 
 
 THE EFFECT OF BACTERIA ON MILK. 
 
 The cow is a much more economical producer of human food than is 
 the steer or the pig, and if bacteria could be prevented from getting into 
 milk, dairying would be a far more remunerative occupation than it 
 now is. 
 
 In milk, for whatever purpose it is to be used, nearly all species of 
 bacteria are detrimental. They not only cause it to sour in a short time. 
 
224 BULLETIN No. 91. [December, 
 
 but make it less wholesome for infants and invalids, as well as often 
 impart a bad flavor. Certain species, however, are essential in the manu- 
 facture of good butter and cheese. 
 
 The changes which bacteria produce in milk are several; the most 
 common, and also the most important one, being the conversion of milk 
 sugar into lactic acid, which is known as souring. Owing to the rapid 
 changes which bacteria cause in milk, it is not, as ordinarily handled, in 
 suitable condition for human food for longer than twelve to forty-eight 
 hours after it is drawn, the time depending upon the temperature at 
 which it is held. It is, then, essential that every family receive daily a 
 fresh supply of milk. This necessitates the expenditure of a large 
 amount of time and labor in delivering the milk. Generally speaking, 
 it costs as much to deliver milk 'to the consumer after it is produced as it 
 does to produce it. From this it is seen that were it not for the action 
 of bacteria, a large supply of milk could be delivered at one time, and 
 thus reduce the delivery to once a week, or even less frequently, which 
 would increase the producer's profit several fold or greatly reduce the 
 price to the consumer. 
 
 When we consider that milk is used daily by all classes of people, it 
 will be seen that the action of bacteria on milk is of the utmost import- 
 ance from a financial standpoint alone. In connection with this, the 
 health of the community should be considered, for disease germs fre- 
 quently find their way into milk where slovenly methods are practiced, 
 and thus endanger not only the health but even the lives of the con- 
 sumers. 
 
 OBJECT OF THE INVESTIGATION. 
 
 The purpose of the investigation reported in this bulletin was to 
 determine the effect of the different common operations performed each 
 day in dairies and dairy barns upon the bacterial content of milk, and to 
 find the most practical methods by which this contamination could be 
 reduced to the least possible amount. 
 
 METHOD USED. 
 
 In this investigation nearly all of the results were obtained by expos- 
 ing petri dishes, which are circular glass dishes with vertical sides having 
 covers similar in shape only large enough to fit easily over the sides, as 
 shown in cut No. 1. The dishes used for this work were one-half inch 
 deep and three and a half inches in diameter, the bottom containing 
 sixty-three square centimeters of surface. These dishes were washed, 
 and sterilized by baking in an oven at a temperature of 140 C. or 284 F. 
 for twenty minutes. Enough sterilized beef broth containing three- 
 fourths of one percent agar was then poured into them to cover the 
 bottoms of the dishes about one-eighth inch deep. The beef broth 
 furnished the nutrient material for the growth of the bacteria, and the 
 
1903.] 
 
 PREVENTING CONTAMINATION OF MILK. 
 
 225 
 
 agar caused it to solidify when cool, so that it would not run when the 
 dishes were tilted. These sterilized dishes were filled with the sterile 
 nutrient medium in a laboratory where the air was comparatively free 
 from bacteria, so that the least possible contamination would take place 
 during filling. The dishes were then held at a warm temperature for 
 two days, so that if any were contaminated they could be easily detected, 
 for in that time the bacteria would have developed into colonies large 
 enough to be visible, and, of course, all dishes not sterile were rejected. 
 
 CUT 1. PETRI DISHES FILLED WITH NUTRIENT MEDIUM, READY TO BE EXPOSED. 
 
 These sterile dishes were kept closed and carried to the place of 
 exposure in a carrying case made for the purpose. An exposure was 
 made, as shown in cuts 2 and 3, by placing a petri dish in a horizontal 
 position, removing the cover for a definite length of time, then quickly 
 replacing it. After being exposed, the dishes were returned to the labo- 
 ratory, where they were held at a warm temperature for three days. 
 Wherever a colony developed it showed that the dish had become con- 
 taminated by one or more bacteria falling on the nutrient medium in the 
 dish at the time of exposure, and by counting these colonies the 
 number of places that bacteria had fallen on the medium was determined. 
 
 That an accurate record of all exposures might be kept, the dishes 
 were numbered consecutively as exposed, and the date, place, condition 
 of exposure, and length of time exposed were recorded. 
 
 In this work the basis taken was the number of colonies developed on 
 sixty-three square centimeters of surface for a half-minute exposure. In 
 some places the exposures were necessarily for a shorter time, or the colonies 
 
226 
 
 BULLETIN No. 91. 
 
 [December, 
 
 would have been entirely too numerous to count. For example, under 
 udders the exposures were usually for only five seconds, and the actual 
 number counted in each case was multiplied by six to bring it to the 
 basis of an exposure of thirty seconds. 
 
 In this investigation 1,185 petri dishes were exposed. As the tables 
 giving a complete record of these exposures are too extensive for publi- 
 cation, and of little general interest, they were condensed by dividing 
 the exposures into groups as far as possible and the average for each 
 
 CUT 2. EXPOSING PETRI DISH IN HANDS UNDER UDDER DURING MILKING. 
 
 group is given. Averages were computed only when several exposures 
 were made at the same time and under similar conditions. 
 
 The first column of each table contains the laboratory number of the 
 dish, or the first number of a group of dishes exposed at the same time 
 and place, and the second column gives the date of exposure. The first 
 column at the right gives the number of exposures averaged, and the 
 remaining column or columns the actual or average number of colonies 
 developed. 
 
1903.] PREVENTING CONTAMINATION OF MILK. 227 
 
 CHECKS ON THE WORK. 
 
 As a further check against error and to learn whether petri dishes 
 might become contaminated before or after direct exposure, certain tests 
 were made. 
 
 January 21, four dishes were carried in the barn for five minutes 
 at a brisk walk without removing the cover. Only one developed a 
 colony, and that but a single one. On the same day one dish stood for 
 
 CUT 3. PETRI DISH CLOSED JUST AFTER BEING EXPOSED UNDER UDDER. 
 
 twenty-five minutes in the barn and another was moved rapidly for five 
 minutes through the dust arising from a pile of fodder freely agitated 
 with a fork. Both covers were left closed, and neither developed a 
 colony. 
 
 Again, twenty-eight dishes stood covered for five days in the dairy 
 building, and twenty-three or eighty-two percent remained sterile. 
 
 March 10, five dishes still in the carrying case stood for one hour 
 in the barn. These same dishes had been standing for five days in the 
 dairy building. Only one dish developed a single colony. From all 
 of which it is concluded that petri dishes are not subject to contam- 
 ination even when in motion in a dusty barn except while the cover is 
 removed. 
 
228 BULLETIN No. 91. [December, 
 
 TABLE 1. BACTERIAL CONDITION OF OUTDOOR AIR. 
 
 Laboratory num- 
 ber of group. 
 
 Date of exposure. 
 
 Place and condition of exposure. 
 
 Exposures aver- 
 aged. 
 
 Colonies 
 developed. 
 
 13 
 
 S3 
 
 H 
 
 (8.S, 
 
 139 
 176 
 177 
 227 
 236 
 237 
 238 
 255 
 256 
 257 
 274 
 276 
 279 
 281 
 325 
 326 
 359 
 398 
 402 
 406 
 
 613 
 634 
 639 
 895 
 905 
 917 
 
 1897 
 March 10 
 April 24 
 
 June 3 
 u 
 
 it 
 u 
 
 u 
 July 2 
 u 
 
 Sept. 14 
 u 
 Oct. 28 
 
 1899 
 May 11 
 May 14 
 
 June 3 
 Sept. 16 
 
 30 rd. from any building 
 
 4 
 2 
 2 
 1 
 1 
 1 
 2 
 1 
 1 
 1 
 2 
 3 
 2 
 1 
 1 
 1 
 2 
 4 
 4 
 1 
 
 14 
 10 
 12 
 10 
 8 
 3 
 
 t 
 
 
 
 
 2" 
 
 & 
 "i 
 
 '3f 
 
 4 
 
 80 
 3 
 18 
 
 4 
 21 
 IS 
 5 
 1 
 1 
 1 
 12 
 17 
 86 
 46 
 
 2J 
 
 Ii 9 o 
 
 'ej 
 
 On post 6 rd. from barn, just after shower . . . 
 Same as No. 176, only at foot of post 
 
 3 ft. from ground 
 
 3 ft. from damp ground, no breeze 
 
 Same as No. 236, only on ground, slight breeze 
 Same as No. 237, only air quiet 
 
 On post 6 ft. from barn, wind from barn .... 
 
 On post, wind blowing across pasture . . . 
 
 3 ft. from ground, 1 rod east of barn 
 
 On ground, 1 rod east of barn 
 
 Same as No. 274, only on post 
 
 On ground 
 
 Same as No. 279, only on post 
 
 On post, 1 rod east of barn 
 
 Same as No. 325, only on ground 
 
 On post in dusty yard, wind from cows 
 
 In dusty yard, wind from grassy field 
 
 In dusty yard among cows, no breeze 
 
 In dusty yard after cows were let out 
 
 Gentle breeze, shower night previous . . . 
 
 On ground in barnyard 
 
 On ground in grassy pasture.! 
 
 On ground in barnyard 
 
 On ground in grassy pasture 
 
 On ground in barnyard .... 
 
 Averaee . 
 
 
 0.9 
 
 IB 
 
 Table 1 shows the average number of colonies that developed in 
 petri dishes from exposures made at different times in the open field and 
 in the barnyard. 
 
 By referring to the column containing the results of exposures made 
 in the open field, it is seen that the group averages range from to 3f 
 colonies, and that the average of the entire forty-three exposures was 
 less than one colony. From the last column, which shows the results of 
 exposures made in the barnyard, it is seen that the group averages range 
 from to 86 colonies, with an average for the fifty-one exposures of 13 
 colonies. Of the exposures made in the open field, fifty percent were 
 sterile, while of those made in the barnyard only twelve percent were 
 sterile, showing that the air in the open field was comparatively free 
 from bacteria, while that in the barnyard, where the ground was bare 
 and dusty, contained more. 
 
1903.] 
 
 PREVENTING CONTAMINATION OF MILK. 
 
 229 
 
 BACTERIAL CONDITION OF AIR IN DAIRY BARNS. 
 The two following tables show the results from exposures made in 
 dairy barns varying in their sanitary condition " and care. They also 
 show the effect upon the bacterial content of the air of the different 
 common operations performed in dairy barns. 
 
 TABLE 2. DAIRY BARN No. 1. 
 
 Frame barn, 30x50 ft., containing two rows of cows; tight floor overhead; 
 plank floor under cows; dirt floor back of cows; cobwebs numerous. 
 
 Place and condition of exposure. 
 
 1.8 
 
 1897 
 
 232 June 15 Barn vacant, open, air still, floor dry 5 
 
 233 Barn vacant, open, air still, floor dry 33 
 
 234 Barn vacant, open, air still, floor dry 19 
 
 235 Barn vacant, open, air still, floor dry 50 
 
 Average 27 
 
 After cows were let in 150 
 
 After cows were let in 54 
 
 After cows were let in 44 
 
 After cows were let in 24 
 
 Average 68 
 
 245 After No. 240, in window, wind blowing out 44 
 
 246 Same as No. 245, only another window 208 
 
 Average 126 
 
 247 In window, opposite side, wind blowing in 4 
 
 248 Same as No. 247, only another window 44 
 
 Average 24 
 
 250 Back of cows, 3 ft. from floor, 30 min. after No. 240. . 34 
 
 252 Back of cows on floor, 30 min. after No. 240 36 
 
 253 4 ft. from floor between two rows of cows 150 
 
 254 " On floor 718 
 
 DAIRY BARN No. 2. H. B. GURLER. 
 
 Barn 50x60 ft., containing four rows of cows; cement floor, wooden stalls, 
 sides and ceiling whitewashed. Milking in progress. 
 
 332 Oct. 20 Middle of west end, cows eating grain and silage .... 2 
 
 336 Northwest corner 51 
 
 337 Northeast corner, wind blowing in 16 
 
 340 Northwest corner 37 
 
 341 Southeast corner 29 
 
 342 Middle of barn 23 
 
 343 Middle of barn 86 
 
 344 Middle of barn 18 
 
 Middle of barn, just after letting out cows 30 
 
 346 Middle of barn, just after letting out cows 26 
 
 Average 32 
 
230 BULLETIN No. 91. [December, 
 
 In Table 2 the result of each exposure is given, and the average of 
 each group is shown in heavy type. 
 
 June 15, when the barn had been vacant, but open for six hours, 
 and the air was comparatively still out of doors, four exposures averaged 
 27 colonies, for so much of the floor was dry and dusty that the air in the 
 barn was far from sterile. After the cows were let in, four exposures 
 averaged 68 colonies, indicating that letting in the cows had increased 
 the bacterial content of the air two and one-half times. Immediately 
 following these, two exposures in a window, wind blowing out, averaged 
 126 colonies, which is nearly twice as many as were obtained from an 
 average of four exposures made at different places in the barn just before. 
 Two exposures in a window, wind coming in, averaged 24 colonies, show- 
 ing that the air was not badly infected when entering the barn, but that 
 it became so while there. 
 
 Exposures Nos. 250 and 252, made back of the cows, showed 34 and 
 36 colonies, while at the same time two exposures made in feed alley 
 between rows of cows showed 150 colonies three feet from the floor, and 
 718 on the floor, from which it appears that there were many more 
 bacteria in the center than at the sides of the barn, and more at the floor 
 than three feet above. 
 
 From the results obtained in this barn we learn that with a dry and 
 dusty floor the bacterial content of the air is high when the cows are in 
 the barn, even though they are not brushed and no hay or bedding is 
 moved. 
 
 At the time the ten exposures were made in dairy barn No. 2, the barn 
 was full of cows eating grain and silage and four men were milking. The 
 number of colonies that developed in the different dishes ranged from 
 2 to 86, with an average of 32. This difference was doubtless due to 
 local conditions, as a cow switching her tail near the exposed dish might 
 send myriads of bacteria into the air at that place. The low average 
 shows that the air was comparatively free from bacteria for a barn full of 
 cows and when milking was in progress. This condition was, no doubt, 
 due to the fact that the barn was built and cared for in a most sanitary 
 manner. An excellent system of ventilation was provided, the cement 
 floor was scrubbed clean every day, sides and ceiling were whitewashed 
 and no cobwebs were allowed to collect. 
 
1903.] 
 
 PREVENTING CONTAMINATION OF MILK. 
 
 231 
 
 TABLE 3. BACTERIAL CONDITION OF AIR IN DAIRY BARN No. 3. 
 
 Stone basement, 32x40 ft., containing two rows of cows; tight floor above, 
 paved floor below; an inch of dusty chaff on floor; cobwebs numerous. 
 
 Laboratory num- 
 ber of group. 
 
 Date of 
 exposure. 
 
 Place and condition of exposure. 
 
 Exposures 
 averaged. 
 
 Colonies 
 developed. 
 
 351 
 
 1897 
 Oct. 25 
 
 Just before cows were let in ; barn vacant all day, 
 except 8 calves in end 
 
 6 
 
 152 
 
 363 
 
 H 
 
 Immediately after cows were let in 
 
 5 
 
 202 
 
 371 
 
 a 
 
 1 hr. after No. 363 
 
 6 
 
 192 
 
 381 
 
 " 
 
 30 min. after No. 371, just after letting out the 
 cows 
 
 4 
 
 150 
 
 387 
 
 Oct. 28 
 
 Conditions same as No. 351 
 
 6 
 
 126 
 
 394 
 
 u 
 
 Window sill, slight breeze blowing in from empty 
 yard 
 
 a 
 
 30 
 
 396 
 408 
 
 a 
 
 u 
 
 After No. 394, in open door, wind blowing out . . 
 Same as No. 394, only 5 min. later, cows having 
 been let in barn in meantime 
 
 2 
 
 ?, 
 
 75 
 39 
 
 410 
 
 u 
 
 Same as No. 408, only in door on opposite side, 
 wind blowing out 
 
 ?, 
 
 66 
 
 412 
 
 " 
 
 30 min. after cows were let in; exposures made in 
 different parts of barn 
 
 fi 
 
 129 
 
 422 
 424 
 
 u 
 u 
 
 30 min. after No. 410, in door wind blowing out. 
 30 min. after No. 408, same window, brisk breeze 
 blowing in from vacant yard 
 
 2 
 ? 
 
 325 
 
 77 
 
 426 
 
 u 
 
 5 min. after No. 422, in door wind blowing out, 
 cows let out in meantime 
 
 2 
 
 321 
 
 428 
 
 " 
 
 In yard below window where No. 424 was ex- 
 posed 
 
 1 
 
 76 
 
 DAIRY BARN No. 4, UNIVERSITY OF ILLINOIS. 
 
 73 
 
 78 
 
 Feb. 13 
 
 u 
 
 After sweeping and feeding, cows eating roughage 
 1 hr. after No. 73, a little bedding put in 20 rain, 
 previous 
 
 4 
 
 o 
 
 94 
 
 72 
 
 83 
 90 
 
 u 
 
 Feb. 23 
 
 20 min. after No. 78, 6 cows brushed in meantime 
 
 After feeding chopped fodder and sweeping, dust 
 visible . 
 
 2 
 6 
 
 692 
 
 84 
 
 96 
 
 u 
 
 40 min. after No. 90; barn quiet in meantime, ex- 
 cept cows eating 
 
 6 
 
 61 
 
 104 
 
 " 
 
 25 min. after No. 96; 13 cows brushed in mean- 
 time . 
 
 10 
 
 159 
 
 121 
 
 March 10 
 
 After feeding and sweeping; doors open, strong 
 wind from south 
 
 6 
 
 40 
 
 127 
 
 H 
 
 1 hr. after No. 121, barn open in meantime, strong 
 breeze from south 
 
 6 
 
 84 
 
 133 
 
 u 
 
 20 min. after No. 127 ; 10 cows brushed in mean- 
 time, barn open, windy 
 
 6 
 
 44 
 
 152 
 
 158 
 
 April 24 
 
 
 
 Cows in, eating oat hay ; barn closed and swept . . 
 1 hr. after No. 152; barn quiet except cows eating 
 hay 
 
 6 
 
 4 
 
 57 
 119 
 
 164 
 
 u 
 
 20 min. after No. 158; 11 cows brushed in mean- 
 time . 
 
 5 
 
 131 
 
 170 
 
 " 
 
 10 min. after No. 164; barn quiet in meantime. . 
 
 1 
 
 53 
 
232 BULLETIN No. 91. [December, 
 
 TABLE 3. BACTERIAL CONDITION OP AIR IN DAIRY BARN No. 4 Continued. 
 
 Laboratory num- 
 ber of group. 
 
 Date of 
 exposure. 
 
 Place and condition of exposure. 
 
 Exposures 
 averaged. 
 
 Colonies 
 developed. 
 
 178 
 
 1897 
 May 4 
 
 Cows in, eating hay; barn closed for 15 min 
 
 6 
 
 62 
 
 184 
 
 
 20 min. after No. 178; 8 cows brushed in mean- 
 time.. 
 
 6 
 
 92 
 
 190 
 206 
 
 June 3 
 
 15 min. after No. 184; barn quiet in meantime . . 
 
 Barn quiet, cows let in, all quiet 15 min.; small 
 amount of bedding in stalls 
 
 3 
 q 
 
 59 
 46 
 
 218 
 
 a 
 
 20 min. after No. 206; 11 cows brushed in mean- 
 time.. 
 
 6 
 
 88 
 
 268 
 
 July 2 
 
 10 cows in, brushed, quiet 15 min., windows open 
 on one side, no wind, damp outside 
 
 6 
 
 12 
 
 285 
 
 July 10 
 
 Cows in, bedded, and fed hay; no rain, and very 
 hot for 10 days 
 
 ? 
 
 55 
 
 316 
 
 Sept. 14 
 
 Milking in progress 
 
 3 
 
 276 
 
 465 
 
 1898 
 Nov. 30 
 
 Barn empty, swept, and closed for 3 hours; snow 
 on ground 3 days 
 
 6 
 
 i 
 
 471 
 
 K 
 
 10 min. after No. 465 . 
 
 fi 
 
 | 
 
 477 
 
 " 
 
 30 min. after No. 465; cows let in, fed chopped 
 fodder; floor swept, dust slightly visible 
 
 1 
 
 236 
 
 478 
 
 a 
 
 30 min. after No. 465; cows let in, fed chopped 
 fodder; floor swept, dust slightly visible 
 
 1 
 
 291 
 
 479 
 
 u 
 
 30 min. after No. 465; cows let in, fed chopped 
 fodder; floor swept, dust plainly visible 
 
 1 
 
 412 
 
 480 
 
 V 
 
 30 min. after No. 465; cows let in, fed chopped 
 fodder; floor swept, no dust visible 
 
 7 
 
 151 
 
 488 
 498 
 
 u 
 
 1 hr. after No. 480; cows eating in meantime. . . . 
 10 min. after No. 488; 16 cows brushed in mean- 
 time ... ... 
 
 9 
 ?, 
 
 84 
 858 
 
 931 
 
 1901 
 June 5 
 
 Milking in progress; no hay moved for 1 hr. ; barn 
 open, slight breeze 
 
 1? 
 
 7i 
 
 282 
 
 1897 
 July 2 
 
 On floor, south door of barn, slight breeze from 
 south, 5 cows in barn 
 
 1 
 
 
 
 283 
 
 
 
 On floor, center of barn, no breeze 
 
 1 
 
 29 
 
 284 
 
 u 
 
 On floor, north door of barn, no breeze 
 
 1 
 
 33 
 
 3?? 
 
 1897 
 Sept. 14 
 
 3 ft. from cow being brushed 
 
 ?, 
 
 800 
 
 497 
 
 1898 
 Nov. 30 
 
 3 ft. from cow being brushed 
 
 1 
 
 600 
 
 487 
 
 u 
 
 Feed room after corn meal was let down from bin 
 above, much dust visible 
 
 1 
 
 20 
 
 500 
 
 Dec. 8 
 
 Feed room after corn meal was let down from bin 
 above, much dust visible . 
 
 4 
 
 4* 
 
 51? 
 
 u 
 
 10 min. after No. 500 . 
 
 ? 
 
 6 
 
 516 
 
 u 
 
 Behind 8 cows just after being brushed 4 min.; 
 less dust visible than at No. 500 
 
 4 
 
 764 
 
 ^99 
 
 u 
 
 5 min. after No. 51C . 
 
 ? 
 
 123 
 
 524 
 
 u 
 
 10 min. after No. 516 . . 
 
 2 
 
 150 
 
1903.] PREVENTING CONTAMINATION OF MILK. 233 
 
 TABLE 3. BACTERIAL CONDITION OF AIR IN DAIRY BARN No. 4 Continued. 
 
 Laboratory num- 
 ber oi group. 
 
 Date of 
 exposure. 
 
 Place and condition of exposure. 
 
 Exposures 
 averaged. 
 
 Colonies 
 developed. 
 
 566 
 
 1899 
 April 13 
 
 Behind cows, milking in progress.. 
 
 2 
 
 60 
 
 59? 
 
 May 11 
 
 Behind cows, milking in progress 
 
 4 
 
 8t 
 
 628 
 
 May 14 
 
 Feed room after musty corn meal was let down 
 from bin above 
 
 ? 
 
 284 
 
 630 
 
 u 
 
 Barn loft 3 min. after hay was moved, small 
 amount of dust visible 
 
 4 
 
 7i 
 
 700 
 
 May 16 
 
 On floor back of cows, milking in progress 
 
 8 
 
 8i 
 
 713 
 717 
 
 May 19 
 
 Barn loft after pitching hay, dust plainly visible . 
 Same place as No. 713 3 min. later. 
 
 4 
 4 
 
 323 
 45 
 
 725 
 721 
 
 
 
 Immediately after No. 717, on beam 8 ft. above. 
 Same place as No. 717, 3 min. later 
 
 2 
 4 
 
 27 
 22 
 
 727 
 
 a 
 
 In feed room after corn meal was let down from 
 bin above, dust plainly visible 
 
 4 
 
 57 
 
 731 
 
 it 
 
 Same place as No. 727, 3 min. later 
 
 4 
 
 15 
 
 735 
 
 
 
 Same place as No. 731, 3 min. later 
 
 4 
 
 12 
 
 739 
 
 
 
 In feed room after bran was let down from bin 
 above, dust slightly visible 
 
 4 
 
 418 
 
 743 
 
 a 
 
 Same place as No. 739, 3 min. later 
 
 3 
 
 6 
 
 830 
 
 Mav 28 
 
 On floor back of cows, milking in progress 
 
 2 
 
 4 
 
 83? 
 
 
 In front of cows, milking in progress 
 
 3 
 
 11 
 
 850 
 
 June 3 
 
 On floor back of cows, milking in progress 
 
 5 
 
 31 
 
 885 
 
 
 After bran was let down from bin above, dust 
 slightly visible 
 
 5 
 
 114 
 
 890 
 
 
 
 Same place as No. 885, 6 min. later 
 
 5 
 
 8f 
 
 927 
 
 Sept. 16 
 
 On floor back of cows, milking in progress.. 
 
 4 
 
 19 
 
 
 
 
 
 
 October 25 and 28, exposures were made in a barn that had 
 been vacant all day excepting eight calves in one end. From the num- 
 ber of colonies which developed it is seen that when the barn floor is 
 dry and dusty, and cobwebs are allowed to collect, the bacterial con- 
 tent of the air is high if there are animals moving about. In such 
 jases the number of bacteria is increased but slightly by letting in the 
 cows. 
 
 These results show that under normal conditions air which enters 
 windows and doors is comparatively sterile, while that which passes out 
 is badly contaminated. 
 
 Barn No. 4 in Table 3 was the University dairy barn before 
 being remodeled. 
 
234 BULLETIN No. 91. [December, 
 
 The floor of the barn was swept each day and no cobwebs were 
 allowed to collect. From the group averages, Nos. 268, 465, 471, and 
 931, it is seen that the bacterial content of the air in the barn was low, 
 even though the cows were in if they were quiet and no hay or bedding 
 had been moved for some time. Immediately after bedding or feeding 
 roughage the number of bacteria in the air was much greater, while an 
 hour later it was reduced about one-third. There were occasional excep- 
 tions to this, as in the three groups on March 10, when all door and 
 windows were open. At the same time there was a strong breeze blow- 
 ing, rapidly replacing the dusty air with air from out of doors, which 
 was nearly sterile. 
 
 To show the effect of having the barn quiet, November 30 all stock 
 was let out, windows and doors closed, and the barn locked for three 
 hours, after which an average of six exposures gave only one-half a 
 colony; ten minutes later, after having moved about in the barn, an 
 average of six exposures gave but five-sixths of a colony. This shows 
 that when the air in the barn remains perfectly quiet for some time, it 
 becomes comparatively sterile. 
 
 Half an hour after letting in the cows and feeding and sweeping, one 
 exposure, where dust was plainly visible, showed 412 colonies, and 
 eleven exposures made at different places in the barn where there was 
 no dust visible, averaged 151 colonies. These results show the number 
 of bacteria that are in the air as a result of feeding and sweeping when 
 the air was nearly sterile before. One hour later nine exposures aver- 
 aged 84 colonies, showing that the dust and bacteria soon settled out of 
 the air. Ten minutes later, sixteen cows brushed in meantime by two 
 men, an average of two exposures gave 858 colonies, showing that 
 brushing the cows had increased the bacterial content of the air over ten 
 times. 
 
 Even though the number of bacteria caught when the cows were 
 eating hay was large, the increase caused by brushing the cows varied 
 from a small amount in one case to over ten times the number in another 
 case, the only exception being when there was a strong breeze blowing 
 through the barn, for in such cases the results are especially uncertain. 
 
 From the table it is seen that the number of bacteria in the air is 
 greatly increased by brushing the cows, and it may also be noticed that 
 the bacteria rapidly settled by allowing everything to remain quiet for 
 from ten to twenty minutes. 
 
 From the latter half of Table 3, beginning with exposure No. 322, it 
 is seen that dust arising from different sources in dairy barns may be 
 similar in amount and yet differ greatly in bacterial content. The 
 average of four exposures made where dust from each of the following 
 sources was plainly visible, contained colonies as follows: corn meal, 57; 
 hay, 323; bran, 418, and from brushing cows, 764. It is seen from this 
 
1903.] 
 
 PREVENTING CONTAMINATION OF MILK. 
 
 235 
 
 that dust which comes from brushing cows contains about twice as many 
 bacteria as that from either hay or bran, and thirteen times as many as 
 dust from corn meal. This is doubtless due to the fact that bacteria 
 find on the cow a good place to develop, as both warmth and nutriment 
 are present. The dust from hay comes from the external and exposed 
 parts of plants, and since bran is from the external portion of the wheat 
 kernel it is natural that the dust from these be heavily laden with 
 bacteria, as the exposed parts of all plants are more or less covered with 
 these organisms Since the great bulk of corn meal comes from the 
 inner portion of the kernel, which is sterile, it is not strange that dust 
 from fresh corn meal contains but few bacteria compared with that from 
 other feeds. The two exposures in dust from musty corn meal, in group 
 No. 628, averaged 284 colonies, while an average of four exposures in 
 fresh corn meal gave in one case 57 colonies, and in another 4 colonies, 
 showing that dust from musty corn meal contains bacteria in much 
 larger numbers than dust from fresh corn meal, as bacteria multiply 
 greatly during the process of fermentation. 
 
 Exposures made a few minutes after a dust had been raised showed 
 in each case that much had settled from the air, and that where 
 there was no movement to keep up a dust, the air soon became compara- 
 tively sterile. 
 
 TABLE 4. BACTERIAL CONDITION OP EXPERIMENTAL MILKING ROOM, UNIVERSITY 
 
 OF ILLINOIS. 
 
 s 
 
 H) 
 
 S 
 
 o 
 G 
 H 
 
 3 
 
 el 
 
 Q 
 
 Place and condition of exposure. 
 
 Exposures aver- 
 aged. 
 
 Colonies devel- 
 oped. 
 
 257 
 
 1897 
 June 25 
 
 Floor damp, sides dry, window open, damp out- 
 doors . 
 
 4 
 
 
 
 261 
 
 July 2 
 
 Window closed, cloudy and damp 
 
 7 
 
 1? 
 
 
 July 10 
 
 Small window open all day, slight breeze .... 
 
 4 
 
 6| 
 
 295 
 
 
 5 min. after No. 289, sides and ceiling sprinkled 
 with hose in meantime 
 
 3 
 
 11 
 
 300 
 
 
 
 Cow being brushed 3 ft. distant 
 
 1 
 
 6174 
 
 301 
 
 " 
 
 After cow had been brushed 4 min. and removed; 
 room quiet 4 min 
 
 ?, 
 
 147 
 
 305 
 
 " 
 
 30 min. after No. 301, room quiet and closed in 
 meantime 
 
 3 
 
 5} 
 
 429 
 
 Nov. 13 
 
 After room had been closed 6 hours 
 
 6 
 
 7| 
 
 435 
 
 
 10 min. after No. 429, just after sprinkling sides 
 and ceiling with hose 
 
 6 
 
 19 
 
 441 
 
 447 
 
 a 
 
 50 min. after No. 435, room closed in meantime. . 
 2 min. after No. 441, cow brought in and brushed 
 1 min 
 
 6 
 
 ?, 
 
 4J 
 
 262 
 
 449 
 
 ii 
 
 After cow had been brushed 4 min. and removed 
 from room 
 
 4 
 
 32 
 
 453 
 
 ii 
 
 3 min. after cow had been removed 
 
 
 11 
 
 455 
 
 ii 
 
 7 min. after No. 453 . 
 
 6 
 
 3 
 
 461 
 
 <> 
 
 8 min. after No. 455 
 
 
 
 
 
 
 
 
 
236 
 
 BULLETIN No. 91. 
 
 [December, 
 
 The results of exposures, shown in Table 4, were obtained in an 
 experimental milking room where the conditions were more completely 
 under control than in the barn ; the purpose being to determine the con- 
 dition of the air in a room that had been vacant for some time, also after 
 sprinkling the sides and ceiling with a hose, immediately after brushing 
 a cow, and at frequent intervals thereafter. 
 
 From this table it is seen that June 25, when the floor of the milking 
 room and the outside air were damp, four exposures were sterile, and 
 July 2 seven exposures averaged If colonies. 
 
 A series of exposures was made under varying conditions July 10 
 and November 13, and from these it is seen that somewhat fewer 
 colonies developed upon entering a room than after thoroughly sprink- 
 ling the sides and ceiling with a hose, as the force of the water seemed to 
 raise a slight dust. This, however, settled rapidly, for as soon as the 
 dust touched any wet surface it adhered to it. July 10 a cow was 
 brought into the nearly sterile air of the room, brushed four minutes, 
 and removed, when exposure No. 300 was made and 6,174 colonies 
 developed. An average of two exposures, group No. 447, made after a 
 cow had been brushed one minute, gave 262 colonies, showing again 
 that the dust which comes from cows is heavily laden with bacteria. It 
 is noticed in both of these cases that the dust rapidly settled when the 
 room remained closed so that there were no currents of air, and in the 
 course of half an hour the air was practically free from bacteria. 
 
 TABLE 5. BACTERIAL CONDITION OF AIR IN DAIRY ROOMS, UNIVERSITY OP ILLINOIS. 
 
 a . 
 
 e 
 
 
 i 
 
 Colonies 
 
 It 
 
 3 
 
 o 
 
 
 1 
 
 developed. 
 
 i| 
 
 a 
 
 i 
 
 Place and condition of exposure. 
 
 U 
 
 
 
 H 
 
 
 <4H 
 
 O 
 
 
 rt 
 
 t> j 
 
 .2 g 
 
 o 
 
 o 
 
 
 2. 
 
 8 
 
 -u O 
 
 r 
 
 di 
 
 R 
 
 
 i 
 
 fcg 
 
 JP 
 
 
 1897 
 
 
 
 
 
 10 
 
 Jan. 13 
 
 On table 
 
 2 
 
 15 
 
 
 11 
 
 
 On table 
 
 2 
 
 
 i 
 
 12 
 
 
 
 On table, milk cooling 
 
 2 
 
 
 
 
 175 
 
 April 24 
 
 On table, room closed for 30 min 
 
 2 
 
 
 
 
 327 
 
 Sept. 14 
 
 On table, milk cooling 
 
 3 
 
 
 1 
 
 330 
 
 
 On table 
 
 1 
 
 14 
 
 
 
 1899 
 
 
 
 
 
 621 
 
 May 1 1 
 
 On table, room empty 
 
 24 
 
 
 A 
 
 625 
 
 
 On table, room empty 
 
 18 
 
 
 
 708 
 
 May 16 
 
 On table when bottling milk 
 
 5 
 
 
 21 
 
 913 
 
 Sept. 16 
 
 On table when bottling milk 
 
 4 
 
 
 
 
 Table 5 shows the average number of colonies developed from expo- 
 sures made in dairy rooms which have cement floors and painted sides 
 and ceilings. From the three exposures made in the front room, which 
 is used both as an office and separating room, the average number of 
 colonies developed was 15. In the bottling room everything is kept 
 
1903.] 
 
 PREVENTING CONTAMINATION OF MILK. 
 
 237 
 
 TABLE 6. COLONIES DEVELOPED FROM EXPOSURES UNDER UDDERS IN VARIOUS 
 
 CONDITIONS. 
 
 Laboratory number of 
 group. 
 
 Date of exposure. 
 
 Number of exposures 
 averaged. 
 
 Average number 
 of colonies de- 
 veloped; 
 different udders. 
 
 Average number of colonies devel- 
 oped; same udder before and 
 after treatment. 
 
 1 
 
 o 
 u 
 
 o 
 '2 
 
 <D 
 ja 
 
 " 
 
 
 $ 
 
 03 
 
 Unwashed. 
 
 Washed. 
 
 Before wash- 
 ing. 
 
 After wash- 
 ing. 
 
 Before wip- 
 ing. 
 
 a 
 
 'Sti 
 
 bJ 
 
 01 
 
 *S 
 
 4H 
 
 < 
 
 198 
 313 
 319 
 331 
 526 
 534 
 
 538 
 554 
 566 
 568 
 574 
 580 
 586 
 592 
 651 
 656 
 671 
 676 
 686 
 690 
 700 
 746 
 751 
 761 
 766 
 776 
 781 
 791 
 793 
 799 
 811 
 817 
 830 
 835 
 850 
 855 
 870 
 920 
 923 
 927 
 
 943 
 
 947 
 955 
 958 
 964 
 967 
 973 
 976 
 996 
 
 1897 
 May 4 
 Sept. 14 
 
 Oct. 20 
 
 Dec. 8 
 u 
 
 1899 
 April 13 
 
 May 11 
 
 May 16 
 
 
 
 
 May 23 
 
 May 28 
 
 June 3 
 
 u 
 
 Sept. 16 
 
 1901 
 
 June 5 
 u 
 
 u 
 u 
 
 June 14 
 
 u 
 
 June 22 
 
 3 
 3 
 3 
 3 
 
 8 
 4 
 
 16 
 11 
 2 
 6 
 6 
 6 
 6 
 4 
 5 
 4 
 4 
 10 
 3 
 8 
 8 
 5 
 10 
 5 
 10 
 4 
 9 
 2 
 4 
 10 
 5 
 9 
 2 
 15 
 5 
 15 
 15 
 3 
 4 
 4 
 
 4 
 8 
 3 
 6 
 2 
 2 
 2 
 4 
 5 
 
 1631 
 
 486 
 219 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 200 
 
 
 
 
 
 
 2973 
 
 
 
 
 
 
 
 90 
 
 
 
 
 
 
 470 
 
 
 
 
 
 
 133 
 
 
 
 
 
 
 
 
 
 60 
 
 
 
 421 
 
 
 
 
 
 
 226 
 
 
 
 
 
 
 211 
 
 
 
 
 
 
 88 
 
 
 
 
 
 
 
 
 
 8* 
 
 
 
 230 
 
 
 
 
 
 
 25 
 
 
 
 
 
 
 157 
 
 
 
 
 
 
 72 
 
 
 
 
 
 
 372 
 
 
 
 
 
 
 152 
 
 
 
 
 
 
 
 
 
 8| 
 
 
 
 25 
 
 
 
 
 
 
 48 
 
 
 
 
 
 
 90 
 
 
 
 
 
 
 11 
 
 
 
 
 
 
 127 
 
 
 
 
 
 
 58 
 
 
 
 
 
 
 
 
 
 6 
 
 
 
 144 
 
 286 
 
 
 
 
 
 
 
 
 
 
 116 
 
 
 
 
 
 
 269 
 
 
 
 
 
 
 
 
 
 4 
 
 33 
 
 
 
 
 
 
 
 
 
 
 
 3 
 
 56 
 
 20 
 27 
 23 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 19 
 
 
 
 
 
 2301 
 
 
 
 
 
 
 503 
 
 
 
 
 1756 
 
 
 
 
 
 512 
 
 
 
 
 
 
 
 1614 
 
 
 
 
 
 
 
 291 
 
 
 
 
 
 
 1026 
 
 
 
 
 
 369 
 
 
 
 
 
 
 1586 
 
238 
 
 BULLETIN No. 91. 
 
 [December, 
 
 TABLE 6. COLONIES DEVELOPED FROM EXPOSURES UNDER UDDERS IN VARIOUS 
 CONDITIONS. Continued. 
 
 Laboratory number of 
 group. 
 
 Date of exposure. 
 
 Number of exposures 
 averaged. 
 
 Average number 
 of colonies de- 
 veloped ; 
 different udders. 
 
 Average number of colonies devel- 
 oped; same udder before and 
 after treatment. 
 
 P 
 
 
 
 
 a 
 | 
 
 1 
 
 A 
 
 a> 
 * 
 X 
 OB 
 
 Unwashed. 
 
 Washed. 
 
 Before wash- 
 ing. 
 
 t* 
 fe- s 
 
 5 
 
 Before wip- 
 ing. 
 
 a 
 
 !i 
 
 * 
 
 1001 
 1011 
 1016 
 1021 
 1031 
 1036 
 1046 
 1051 
 1061 
 1066 
 1095 . 
 1100 
 1110 
 1115 
 1125 
 1130 
 1140 
 1145 
 1155 
 1160 
 1170 
 1175 
 Numbe 
 avers 
 
 Averae 
 
 June 22 
 June 24 
 
 
 
 a 
 
 u 
 
 June 27 
 
 
 
 u 
 
 June 28 
 
 H 
 U 
 
 r of exposur 
 Lffed 
 
 10 
 4 
 5 
 10 
 4 
 10 
 5 
 10 
 5 
 8 
 5 
 9 
 4 
 9 
 3 
 8 
 5 
 10 
 4 
 9 
 5 
 10 
 es 
 
 
 
 
 
 
 346 
 
 
 1401 
 
 
 
 
 
 
 
 
 482 
 
 iis 
 
 i23 
 i33 
 
 229 
 '421 
 '262 
 
 
 
 
 
 
 
 
 
 
 120 
 
 
 
 
 
 
 
 
 
 202 
 
 
 
 
 
 
 
 
 
 94 
 
 
 
 
 
 
 
 
 
 266 
 
 
 
 
 
 
 
 
 
 114 
 
 
 
 
 
 
 
 
 
 448 
 
 
 
 
 
 193 
 
 'igi 
 
 '313 
 '407 
 
 
 
 
 
 
 329 
 
 
 
 
 
 
 
 
 
 849 
 
 
 
 
 
 
 
 
 
 314 
 
 
 
 
 
 
 
 
 
 
 26 
 
 42 
 
 74 
 
 103 
 
 58 
 
 117 
 
 27 
 
 e . 
 
 362 
 
 83 
 
 615 
 
 148 
 
 630 
 
 270 
 
 12 
 
 scrupulously clean, and the floor is usually damp, thus keeping the 
 greater part of the dust out of the air. Sixty exposures were made in this 
 room at different times of the year, and the average for the total number 
 was one-third of a colony. More than half of all colonies developed from 
 the bottling room were from five exposures made when bottling milk; 
 forty-seven of the sixty exposures in this room were sterile. In other 
 words, a dish would have to be exposed an average of one and a half 
 minutes to catch one bacterium. In an atmosphere as nearly sterile as 
 this, milk becomes contaminated very slowly, even where a large surface 
 is exposed, as in passing over a cooler. 
 
 To learn something of the amount of contamination that takes place 
 during milking, and how much this may be reduced by washing the 
 udders, 420 petri dishes were exposed under washed and unwashed 
 udders. The average number of colonies developed from exposures 
 made under washed udders was 192 and under unwashed udders 578, 
 or three times as many. The group averages from these exposures are 
 shown in Table 6. 
 
1903.1 
 
 PREVENTING CONTAMINATION OF MILK. 
 
 239 
 
 As a rule, washing udders makes a marked reduction in the number 
 of colonies developed from exposures made under them. This difference 
 is much greater in some cases than in others. The most noticeable 
 
 CUT 5. IN MID-WINTER. 
 
 PROPERLY CLEANED.'TO, PREVENT ALL/ POSSIBLE 
 CONTAMINATION " 
 
 difference was obtained December 8, when an average of eight expo- 
 sures, No. 526, showed 2,973 colonies before washing, while an average 
 of four exposures made under the same udder after washing showed only 
 90 colonies. In other words, the contamination which took place'in this 
 instance was thirty-three times greater before washing than after. 
 
 In a few cases a less number of colonies developed from exposures 
 made under unwashed udders than from those made under the same 
 udders^after washing. A possible explanation" for this is that dirt from 
 
240 
 
 BULLETIN No. 91. 
 
 [December, 
 
 the unwashed udders fell in larger particles, and thus the dishes were 
 contaminated in fewer places, although a greater total contamination 
 took place, for a colony developed on a petri dish may have originated 
 
 CUT 6. AFTER A RUN OF THREE WEEKS ON PASTURE. IMAGINE THE SOURCE OF 
 CONTAMINATION DURING WINTER. 
 
 from a single bacterium or from a particle of dirt large enough to be seen 
 with the naked eye and containing thousands of bacteria. 
 
 It should be borne in mind that the udders used in this experiment 
 were not only apparently clean, but they had been washed regularly each 
 day before milking, and in all probability there was much less dirt 
 adhering to them than to udders that had never been washed. With 
 soiled or muddy udders, such as are frequently found in dairies, the 
 benefits derived from washing are much greater than these results show. 
 
1903.] 
 
 PREVENTING CONTAMINATION OF MILK. 
 
 241 
 
 IM CO (M 1-1 <N <N 
 
 i 
 
 be 
 
 OO^F>OGOOi-HT-<i ilOcOOCOCOi irHT^-^tioOOOOOOOi i i I i i i I ?3 
 --l(N(M(NeOCOCO?OlN(N(N <M(N<N<N'-H.-ii-H,-i<M(N<N<N ft 
 
 OOOOi-iOt-iOOOO^HT (i ii ii lOi i(N<Nr-(rH(NCO' 
 
 1-1 03 
 
 ...S-4 
 
 HD t> t CJ W O 00 
 
 < i 
 
 i (M (N IM(M iM <N 
 
242 
 
 BULLETIN No. 91. 
 
 [December, 
 
 o 
 
 I 
 
 3 
 
 o w 
 M 
 
 s 
 
 H 
 
 w . 
 2 v 
 
 SB 
 
 i 
 ^ 
 
 ^^ 
 
 i 
 
 w 
 PQ 
 
 O 
 
1903.] PREVENTING CONTAMINATION OF MILK. 243 
 
 WEIGHT OF DIRT WHICH FALLS INTO MILK DURING MILKING. 
 
 The results shown in Table 7 were obtained for the purpose of deter- 
 mining by weight the amount of filth which falls into milk during the 
 process of milking, and how much this may be reduced by washing the 
 udders. 
 
 After several trials with three different milkers on thirty cows, it was 
 found that it required an average of 4 minutes to milk a cow. A glazed 
 dish, eleven inches in diameter, the size of an ordinary milk pail, was 
 held under a cow's udder 4 minutes, while the milker went through 
 motions similar to those made in milking, but not drawing any milk. 
 The amount of dirt which fell into the dish during the operation was, of 
 course, approximately the same as would have fallen into the milk during 
 the milking process. The dirt caught in the dish was then brushed into 
 a small glass weighing tube, such as shown in cut 9, the udder washed, 
 and the process repeated. Both tubes were then placed in a desiccator, 
 and after drying twenty-four hours to remove moisture, were accurately 
 weighed in a chemical balance. 
 
 It will be noticed that the weight of dirt which fell from udders 
 varied greatly when there appeared to be the same amount on them. 
 The reason for this is that the amount of dirt which falls from a clean, a 
 soiled, or a muddy udder depends upon the character of the dirt, the 
 amount of hair on the udder, its shape, the length of the teats, etc. 
 
 Seventy-five trials were made at different seasons of the year with 
 three classes of udders, those apparently clean, soiled, and muddy. 
 With udders that were apparently clean, it was found that an average of 
 3 times as much dirt fell from the unwashed udders as from the same 
 udders after they were washed. With soiled udders the average was 18, 
 and with muddy udders 90 times as much dirt from the unwashed as 
 from the washed. 
 
 The average weight of dirt falling from muddy udders during the 
 time of milking was found to be .8831 of a gram. Since in one ounce 
 there are 28 grams, an ounce of dirt would fall into the milk for every 
 32 milkings. From a year's records, kept by the department of dairy 
 husbandry, of eight herds containing 144 cows, it was found that one 
 gallon, or 8f pounds, was the average yield at a milking. On this basis, 
 in 32 milkings, 275 pounds of milk would be produced containing one 
 ounce of filth. With the same udders after they were washed, 24,030 
 pounds of milk, or 90 times as much, could be obtained before the] 
 amount of filth it contained would reach one ounce. This shows the 
 decided advantage, in the production of clean milk, of washing the 
 udders before milking. 
 
244 
 
 BULLETIN No. 91. 
 
 [December, 
 
 CUT 9. PETRI DISH, SHOWING COLONIES DEVELOPED FROM EXPOSURE DURING 
 MILKING IN WELL-KEPT DAIRY BARN. 
 
 TABLE 8. AVERAGE NUMBER OF COLONIES DEVELOPED FROM EXPOSURES MADE IN 
 
 DIFFERENT PLACES AND TIME MILK WOULD HAVE TO STAND AT THOSE 
 
 PLACES TO RECEIVE AS MUCH CONTAMINATION FROM THE 
 
 AlR AS IT WOULD UNDER AN UNWASHED UDDER 
 
 DURING THE 4 MlNUTES OF MlLKING. 
 
 
 
 
 Ave. number min. 
 
 
 
 Num- 
 
 Average 
 
 milk would have to 
 stand at the different 
 
 
 Place of exposure. 
 
 expo- 
 sures 
 aver- 
 aged. 
 
 colonies de- 
 veloped 
 from Vz min. 
 exposure. 
 
 places to receive as 
 much contamination 
 from the air as it 
 would under an un- 
 washed udder during 
 
 Time in 
 days. 
 
 
 
 
 the 4 J- min. of milking. 
 
 
 Open field 
 
 43 
 
 A 
 
 2890 
 
 2 
 
 Barnyard . . . 
 
 51 
 
 13 
 
 200 
 
 
 Well kept barn during milking . . 
 University barn during milking . 
 
 10 
 46 
 
 32 
 
 38 
 
 81 
 68 
 
 ''\ 
 
 Poorly kept barn during milking 
 
 21 
 
 168 
 
 15 
 
 
 Barn empty, closed 3 hours .... 
 
 12 
 
 
 
 3901 
 
 2$ 
 
 Before feeding 
 
 9 
 
 46 
 
 57 
 
 
 After feeding 
 
 34 
 
 109 
 
 24 
 
 
 After brushing cows 
 
 38 
 
 307 
 
 8 
 
 
 Under apparently clean unwash- 
 
 
 
 
 
 ed udder 
 
 158 
 
 578 
 
 4A 
 
 
 Under washed udder 
 
 262 
 
 192 
 
 14 
 
 
 Bottling room 
 
 60 
 
 i 
 
 7803 
 
 55 
 
 Dairy front room. . 
 
 3 
 
 15 
 
 173 
 
 
 
 
 
 
 
1903.] 
 
 PREVENTING 'CONTAMINATION OF MILK. 
 
 245 
 
 CUT 10. PETRI DISH, SHOWING COLONIES DEVELOPED FROM EXPOSURE DURING 
 MILKIXG IN POORLY KEPT DAIRY BARN. 
 
 CONCLUSIONS. 
 
 The results of the work described in this bulletin are of vital impor- 
 tance to the practical dairyman, as they show that extreme cleanliness 
 is absolutely essential to the most successful dairying. 
 
 Table 8, which contains averages of all exposures made in different 
 places, shows where and under what conditions milk becomes contami- 
 nated most rapidly, and that the bacterial content of milk may be 
 greatly reduced by a few simple precautions easily carried out in any 
 dairy. The nearer the ideal condition is reached, the fewer bacteria in 
 the milk, and the more wholesome will be not only the milk itself, but 
 the products made from it, 'and the better their keeping quality. 
 
 From exposures made out of doors it was found that air in the open 
 field was nearly sterile, since an average of less than one colony devel- 
 oped for each half-minute exposure, while in the barnyard an average 
 of 13 colonies developed in the same time. This increase over the num- 
 ber in the field was doubtless due to the fact that the ground in the 
 barnyard was bare and dry, and the cows moving about created a dust. 
 
 In a well-kept dairy barn, where the floor was swept clean and no 
 
246 
 
 BULLETIN No. 91. 
 
 [December, 
 
 cobwebs were allowed to collect, 32 colonies developed from exposures 
 made when milking was in progress, and in a poorly kept barn, where 
 there was much dust on the floor and cobwebs were numerous, 168 colo- 
 nies developed, or five times as many. This shows the decided advan- 
 tage of keeping the dairy barn as clean as possible. 
 
 To show the effect of having everything in the milking stable quiet 
 for some time, the University dairy barn was swept, after the cows were 
 
 CUT 11. PETRI DISH, SHOWING COLONIES DEVELOPED FROM EXPOSURE 
 UNDER APPARENTLY CLEAN UNWASHED UDDER. 
 
 let out, and closed for three hours; exposures then made showed an 
 average of less than one colony. 
 
 When the cows were in, but before feeding, 46 colonies developed for 
 each half-minute exposure; immediately after feeding roughage 109 
 colonies developed, and after brushing the cows the number was 
 increased to 307. These results indicate that feeding roughage and 
 brushing cows greatly increase the bacterial content of the air. Such 
 operations, therefore, should not take place immediately before milking, 
 but some time should intervene to allow the dust to settle. 
 
 By far the greatest source of contamination in milk is the cow her- 
 self, and the greater part of this contamination comes from the udder, 
 unless that is washed before milking. The one hundred fifty-eight 
 
1903.] PREVENTING CONTAMINATION OP MILK. 247 
 
 exposures made under unwashed udders averaged 578 colonies, or three 
 times as many as the average number developed from exposures made 
 under the same udders after washing. Table 7, giving the weight of dirt 
 caught under udders in different conditions, shows that three and one- 
 half times as much dirt fell from apparently clean unwashed udders as 
 from the same udders after washing. Thus it is seen that in the case of 
 apparently clean udders the ratio of the weight of dirt caught corre- 
 
 CUT 12. PETRI DISH, SHOWING COLONIES DEVELOPED FROM EXPOSURE 
 UNDER WASHED UDDER. 
 
 sponds very closely with the ratio of the number of colonies developed 
 from exposures under washed and unwashed udders. The amount of 
 contamination from soiled or muddy udders was not determined from a 
 bacteriological standpoint; the benefit derived from washing such udders 
 was determined only by the comparative weights of dirt caught under 
 them. With soiled udders the weight of dirt was eighteen times greater 
 from the unwashed udders than from the same udders after washing, and 
 with muddy udders it was ninety times greater. 
 
 In the University of Illinois dairy rooms, which have cement floors 
 and painted sides and ceilings, there are comparatively few bacteria in 
 the air. This is especially true of the milk bottling room, where the floor 
 
248 BULLETIN No. 91. [December, 
 
 is frequently scrubbed, and is usually damp, as an average of sixty expo- 
 sures showed only one-third of a colony. 
 
 From the averages in the preceding table it is seen that the amount 
 of contamination that milk receives from the bacteria of the air falling 
 into it, depends entirely upon the conditions under which it was 
 exposed. The table also shows the length of time it would take milk 
 exposed in the pail to receive the same amount of contamination at the 
 designated places that it gets from an unwashed udder during milking, 
 
 CUT 13. PETRI DISH, SHOWING COLONY DEVELOPED FROM EXPOSURE IN 
 MILK BOTTLING ROOM. 
 
 which time was found to be 4 minutes. Since an average of 578 colo- 
 nies developed on sixty-three square centimeters of surface for every 
 half-minute exposure under an unwashed udder, in 4^ minutes the 
 number would have increased to 5,202. In the milk bottling room an 
 average of one-third of a colony developed on a like area for every half- 
 minute exposure, or two- thirds per minute. A pail of milk would, there- 
 fore, have to stand exposed to the air in this room 7,803 minutes, or 
 more than five days, to receive as much contamination as it would 
 under an apparently clean unwashed udder during milking. This 
 emphasizes not only the great importance of washing the udders before 
 
1903.] PREVENTING CONTAMINATION OF MILK. 249 
 
 milking, but also of having the dairy rooms and all surroundings as clean 
 and the air as free from dust as possible wherever dairy products are 
 handled. 
 
 An effort was made to determine the different species of bacteria that 
 gain access to milk, but in the present state of development of the science 
 of bacteriology, this is difficult to do satisfactorily. For the practical 
 dairyman it is sufficient to say that a majority of the forms found grow 
 readily in milk. Many of the species produce visible changes in milk, 
 such as curdling or peptonizing, while others affect the flavor. 
 
 It should be borne in mind that a great majority of the species of 
 bacteria that gain access to milk do not possess the power to produce 
 disease, and are not injurious to healthy adults, although many of them 
 are likely to produce disorders of digestion in infants and invalids. 
 
 Paying special attention to cleanliness in every step of the production 
 and care of milk will result not only in clean milk, but in a marked 
 reduction in the number of bacteria it contains, which will greatly 
 lengthen its keeping qualities. That the desired results may be 
 obtained, care must be constantly exercised. It is of little consequence 
 to practice extreme cleanliness in all of the steps of milk production but 
 one, and be filthy about that one, as this spoils the whole. Even if the 
 majority of species of bacteria which ordinarily gain access to milk are 
 not dangerous to health, no one cares to consume milk in which a sedi- 
 ment is found at the bottom if it is allowed to stand for a short time. 
 Frequently much filth is allowed to get into milk during milking, and 
 many milkers practice the filthy habit of keeping the teats wet with milk 
 during the milking process, yet after it is drawn the greatest care is 
 exercised that no dust or dirt gain access to it. As far as the final result 
 is concerned, all painstaking care in the subsequent operations is lost 
 because of the careless work at the beginning during the process of 
 milking, for if filth once gains access to milk, no amount of care after- 
 wards can remedy the difficulty. It is, therefore, of the greatest impor- 
 tance to the advancement of better dairying that special emphasis be 
 placed upon the operation where milk is liable to receive the most con- 
 tamination. The work reported in the preceding pages shows that the 
 greatest source of contamination in milk, as ordinarily produced, is the 
 cow herself, and this is doubly important because it is the source which 
 is given the least attention in actual practice. 
 
UNIVERSITY OF ILLINOIS-URBANA