EXPERIMENT STATION BULLETINS. 289 



of the subject can be adjusted to exactly fit his case. The author trusts that in the 

 further discussion of this subject he will be rightly interpreted as to his motives 

 and ideas. The purity of milk is dependent upon the milking process itself and its 

 surroundings, for pure milk once obtained, it can be kept comparatively pure for some 

 daj-s and is capable of management according to the will of the dairyman. 



The author has aimed by some simple experiments to demonstrate the real significance 

 of what is meant by pure milk and polluted milk. He will call to his aid the work of 

 others to assist in verifying his conclusions. The experiments of the author were car- 

 ried out under average conditions of dairy operations and the results may readily be 

 taken as average results. Those quoted from other authors or investigators will 

 be cited in sufficient detail to convey a fair understanding. 



A sterile glass dish one-half inch in depth and three and one-half inches in diameter, 

 with an overlapping cover, was exposed in the air of the milking stable for five minutes. 

 After the exposure, nutrient gelatin, a suitable food for most bacteria, was added to 

 the dish and allowed to solidify. The dish was then placed away at the ordinary 

 room temperature of the laboratory that the life in the dust which fell into the uncov- 

 ered sterile dish for five minutes might develop. Each germ present usually grows 

 into a colony which may be readily seen with the naked eye or by means of a very low 

 magnifying glass. When these colonies are counted a fair idea is obtained of the 

 number of bacteria present in the dust. However, many fine particles of dust do not 

 dissolve in this gelatin, a fact which is easily determined by the microscope, so that 

 only a fraction of the entire number of micro-organisms is represented. The germs 

 on the surface may grow into colonies, but those that are contained within the particle 

 are removed from the food material, hence have no opportunity for development. 

 Remembering the above description and explanation it will be readily understood how 

 the number of bacteria is obtained and how inadequate is this crude method. Other 

 methods more exact are in use, but are more technical and thus are not so desirable 

 for the present purpose. 



Several exposures were made in the open air of the stable and the number of colonies 

 developing in each plate, or the approximate number of micro-organisms present in the 

 dust of each plate, exposed for five minutes, varies from twelve to eighteen thousand in 

 round numbers. These exposures were made when milking was in progress. The ordinary 

 milk pail is about twelve times as large at the top as is the little glass dish mentioned 

 above, accordingly the approximate number of micro-organisms falling into the pail 

 exposed to the stable dust for five minutes would be twelve times as great, or from one 

 hundred forty-four hundred or fourteen thousand four hundred to twenty thousand 

 six himdred. 



Had this estimation been made at the time of feeding dusty foods, or when bedding 

 the cows with straw, or when the cows were entering the stable, the number would 

 have been Tuarkedly increased. It was not the purpose of the writer at the time to 

 take up all the possibilities incident in the management of a dairy stable, for he is 

 reserving such investigation for a future time. It may be confidently stated that 

 a few estimations made at such a time as above mentioned indicate what has been 

 demonstrated by Hesse, that the increase is very great. 



Aside from the probabilitj^ that milk setting in a stable absorbs obnoxious gases, 

 the importance of the germ content of the air of the cow stable is readily seen by 

 these simple experiments. As a general statement it may be safe to say that the 

 smaller the number of germs in the milk the better will be its keeping qualities. If, 

 as is often done, the milk is allowed to stand in the pail exposed to the air of the 

 stable for thirty minutes the number would be si.x times as great, or varying from 

 eighty-six thousand four hundred to one million two hundred thirty-six "thousand. 

 Even so far as the dust of the stable air is concerned, every minute of time is very 

 significant. Had the dust arising from feeding, or bedding, or grooming, or, in short, 

 any disturbing influence, been added, what might occur is almost beyond prediction. 



A single cow's hair has its role to play. Estimations have been made of the germ 

 life pros'Tit on cami)arMtiveIy e]e;in hairs taken from cows. There was no desire to tako 

 hairs which had little lumps of dung on, for no satisfactory idea could be obtained 

 in this manner. Hairs were secured from the side and top of the cow and at a dis- 

 tance from iiianurial putc-hes of ricliiiess. Our estiinatos demonstrate that from six 

 to seven hundred micro-organisms, approximately, may be found on what may be re- 

 garded as clean hairs. 



If by means of one, two, three or fo-ir thicknesses of cheese elotli. or by an additional 

 layer of cotton wool, the diaryman removes the hairs from the milk, he thinks he has 

 removed the evil. It would be just as rational to secure a bunch of hairs from a cow, 

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