THE RELATION OF MICROORGANISMS TO MILK 435 



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

 to the fact that immediately after secretion the milk becomes contami- 

 nated by bacteria which exist in the interior of the udder. Early inves- 

 tigators, notably de Freudenreich and Grotenfelt, believed that milk 

 while in the udder was entirely free from microorganisms. Later inves- 

 tigations, however, by Moore, Ward, Bolley, Hall and others, have 

 shown that the healthy udder normally 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 se- 

 creting cells. These organisms, which normally exist in the milk pas- 

 sages 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. 138). The number of bacteria found 

 in the udder varies widely in different cows as may be seen by the 

 following figures: 



v 



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 1)850 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 of " 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 strippings, 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. 



