SOURCES OF COMMON MILK BACTERIA 



59 



and her udder not injured in any way, the milk she secretes is 

 at the moment of secretion free from bacteria. 



This question is of far less importance than might seem 

 likely, for whatever may be the condition of the milk when 

 secreted, it is never sterile at the time it leaves the udder. Bac- 

 teria are known to be abundant . 

 in the udder. These bacteria 

 probably come from without, 

 entering through the teat into 

 the milk ducts, feeding perhaps 

 on the remains of the milk that 

 clings to the passages between 

 the different milkings. 1 How far 

 into the ducts these bacteria ex- 

 tend is again a matter of differ- 

 ence of opinion. 2 Some have 

 held that they are in all the 

 ducts in the glands; others in- 

 sist that the inner ducts are 

 germ free in normal cows. 3 

 (Fig. 30.) But these great dif- 

 ferences of opinion are of no 

 great practical importance, for 

 bacteria are certainly present 

 in the milk ducts, so that the 

 milk, 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 



Ward. Bui. 178, Cornell Exper. Sta., 1898. 



2 Simon. Hyg. Rund., X., p. 71, 1900. 



Harrison. Jour. Ap. Microscopy, V., pp. 20-29, 1903. 



3 Freudenreich. Cent. f. Bact., II., x., p. 401, 1903; xiii., p. 281, 1904. 

 Uhlmann. Rev. Gen. d'Lait., iii., p. 163, 1904. 



Russell and Hastings. Ann. Rep. Wis. Exper.. Sta., p. 164, 1904. 



FIG. 30 STRUCTURE 



UDDER 



Showing ducts in which 

 grow 



CO\V S 



bacteria 



