298 MICROBIOLOGY OF MILK AND MILK PRODUCTS. 



does not contain bacteria in greater or less numbers. This is due to the 

 fact that immediately after secretion the milk becomes contaminated by 

 bacteria which exist in the interior of the udder. Early investigators, 

 notably de Freudenreich and Grotenfelt, believed that milk was entirely 

 free from microorganims. Later investigations, however, by Moore, 

 Ward, Bolley, Hall and others, have shown that the healthy udder nor- 

 mally contains bacteria in appreciable numbers. It has been found that 

 bacteria are present even in the upper portions of the udder in the small 

 milk passages leading from the secreting cells. These organisms, which 

 normally exist in the milk passages of the udder, gain entrance through 

 the orifice in the end of the teat where they find suitable conditions for 

 growth and, once inside, work up through the milk cistern to the larger 

 milk ducts and finally though all parts of the udder (Fig. 73). The 

 number of bacteria found in the udder varies widely in different cows 

 as may be seen by the following experiments: 



Bacterial Content of Entire Milk of Different Cows. 



Cow No. i, 850 bacteria per c.c. 



Cow No. 2, 750 bacteria per c.c. 



Cow No. 3, 25 bacteria per c.c. 



Cow No. 4, 112 bacteria per c.c. 



Cow No. 5, 70 bacteria per c.c. 



Cow No. 6, 1850 bacteria per c.c. 



If portions of milk are taken at different intervals during the process 

 of milking in such a way that all external contamination is prevented, it 

 will be found that the first few streams- or "fore-milk" contain many 

 more organisms than the milk drawn later. After the first ten or twelve 

 streams the number of organisms will decrease quite rapidly, normally 

 becoming less and less until the final stoppings, when there is usually a 

 marked increase. This condition indicates that the larger number of 

 organisms exist in the milk cistern and larger milk ducts in the lower 

 part of the udder and are therefore removed during the early part of the 

 milking. The increase at the end of the milking is probably due to the 

 greater manipulation, resulting in dislodging some of the organisms 

 which have adhered to the walls of the milk passages. 



Not only does the number of organisms in different cows vary, but 

 there is a marked difference in the different quarters of the same udder, 

 as shown by the following figures: 



