4 THE CONTAMINATION OF MILK. 



organism in milk, and have observed that it is identical with, 

 or closely allied to, Micrococcus pyogenes aureus {staphylococcus 

 pyogenes aiireus} . Willem and Minne likewise regard these 

 organisms, found in freshly drawn milk, as M. pyogenes (68). 

 Streptococci, indistinguishable from Streptococcus pyogenes, 

 have been isolated from milk taken from the normal udder 

 under aseptic precautions (47). They have been observed in 

 the milk of a cow in the Cornell University dairy herd for a 

 period of two years and a half, during which time there was 

 no occurrenc^ <)f udder trouble. This streptococcus when 

 injected int6 a healthy udder produced mammitis. The ex- 

 cellent record of milk production for several years previous 

 gave assurance that the animal had not suffered a severe attack 

 of streptococcus infection of the udder (47). A number of 

 species have been described as occurring in freshly drawn milk, 

 but the variety of species is very much restricted as compared 

 with those encountered in market milk. 



Significance. The presence of bacteria within the udder con- 

 stitutes an obstacle to the production of absolutely sterile milk. 

 v. Freudenreich collected samples, with aseptic precautions, at 

 the beginning, the middle and the end of the milking, deter- 

 mining the number of bacteria present. The average results of 

 185 determinations gave for the beginning, 6505 per cc.; for 

 the middle, 1341 percc.; and for the end, 769 percc. Kuntze 

 (Ref. .22, Chap. II) obtained an average of 419 per cc. from 

 40 samples of freshly drawn milk taken at different times dur- 

 ing a year. Some very careful American work has shown that 

 the contamination of the whole milking, mostly from within 

 the udder, may vary from 200 per cc. to 900 per cc., depending 

 upon the cow, the average being about 500 per cc. The 

 methods' of aseptic production of milk have reached such a 

 point of refinement in some dairies that the bacteria unavoid- 

 ably introduced from the udder constitute the bulk of the 

 bacteria present in the product when bottled. The occurrence 

 of micrococci and streptococci in milk in the udder is a circum- 

 stance that certainly cannot justly be attributed to carelessness 

 in milk production. Nevertheless, in some cases the contam- 

 ination from this source has been lessened by avoiding the use 



