Practical dairy bacteriology, prepared for the use of students, dairymen, and all interested in the problems of the relation of milk to public health . s question is of far less importance than might seemlikely, for whatever may be the condition of the milk whensecreted, it is never sterile at the time it leaves the udder. Bac-teria are known to be abundantin the udder. These bacteriaprobably come from without,entering through the teat intothe milk ducts, feeding perhapson the remains of the milk thatclings to the passages betweenthe diiiferent milkings.^ How farinto the ducts these bacteria e
Practical dairy bacteriology, prepared for the use of students, dairymen, and all interested in the problems of the relation of milk to public health . s question is of far less importance than might seemlikely, for whatever may be the condition of the milk whensecreted, it is never sterile at the time it leaves the udder. Bac-teria are known to be abundantin the udder. These bacteriaprobably come from without,entering through the teat intothe milk ducts, feeding perhapson the remains of the milk thatclings to the passages betweenthe diiiferent milkings.^ How farinto the ducts these bacteria ex-tend is again a matter of differ-ence of opinion.^ Some haveheld that they are in all theducts in the glands; others in-sist that the inner ducts aregerm free in normal cows.(Fig. 30.) But these great dif-ferences of opinion are of nogreat practical importance, forbacteria are certainly presentin the milk ducts, so that themilk, even though sterile when secreted, is practically sure to be contaminated by bacteria be-fore it reaches the mouth of the milk duct. It is thus very dif-ficult to draw sterile milk from the cow in spite of the greatest. FIG. 30—STRUCTUREUDDER Showing ducts in whichgrow OF cows bacteria Ward. Bui. 178, Cornell Exper. Sta., Simon. Hyg. Rund., X., p. 71, 1900. Harrison. Jour, Ap. Microscopy, V., pp. 20-29, 1903.« Freudenreich. Cent. f. Bact., II., x., p. 401, 1903; xiii., p. 281, Uhlmann. Rev. Gen. dLait., iii., p. 163, 1904. Russell and Hastings. Ann. Rep. Wis. Exper. Sta., p. 164, 1904. 1904. 6o PRACTICAL DAIRY BACTERIOLOGY care. By extreme precautions in special tests small quantitiesof sterile milk have been thus obtained; but these precautionsare not practical in ordinary milking, so that the dairymanmust recognize that he cannot by any means of milking obtainsterile milk. Bacteria in the Milk Ducts.—The types of bacteria whichcome from the milk ducts are varied. They are mostly cocciand usually are not very numerous. Some of them liquef
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