70 Milk and Its Products. 



and appear in the milk. If the udder is the seat 

 of disease due to the growth of bacteria, such bac- 

 teria may find their way into the milk ducts and 

 infect the milk. In one other waj' the animal may 

 be said to be a source of infection with bacteria. 

 •The end of the teat of the animal is always more 

 or less moist. Bacteria coming in contact with 

 such surface, moistened with milk, find there not 

 only food in proper form for their growth, but a 

 temperature sufficient to make them active. They 

 begin to multiply, and, working their way through 

 the orifice of the teat, find milk in larger supply, and 

 a temperature still more favorable for their growth. 

 They increase and multiply, under such conditions, 

 with remarkable rapidit}', and so work their way 

 upward through the milk cistern and into the larger 

 milk ducts, so that the milk first drawn from the 

 animal alwaj'S contains a greater or less number of 

 bacteria. For this reason it is not an easy matter 

 to secure perfectly sterile milk direct from the cow, 

 though w^ith great care in disinfecting the udder 

 and removing the larger part of the milk from it, 

 perfectly sterile milk has been obtained. 



Kinds of bacteria in milk. — Almost any of the 

 known forms of bacteria may live and grow and oc- 

 casionally be found in milk. Normally, however, com- 

 paratively few forms of bacteria are present. The 

 greater part of these are forms which cause various 

 changes in the constituents of milk, and are known 

 as ferments, and the changes which they induce as 

 fermentations. Beside these fermentations, there may 



