MICRO-ORGANISMS IN MILK 269 



in the udder is weighed, the conclusion becomes inevitable that 

 bacteria are constantly present in the udders of normal animals. 

 The number of bacteria may vary, of course, within wide limits, 

 and when relatively few are present it is perhaps possible to 

 obtain milk that contains very few bacteria from the higher parts 

 of the udder and that sometimes may be germ free. 



Since bacteria probably do not pass through healthy mammary 

 glands, the source of micro-organisms in the udder must be sought 

 elsewhere. The most obvious portal of entry is the teat canal. 

 The small portion of milk remaining in the teat duct, the favor- 

 able temperature, and the protecting folds of the membrane 

 afford ample opportunity for bacteria to multiply in the duct. 

 The aperture of the teat comes in contact with substances that 

 carry bacteria, such as bedding, fodder, and dust, for example. 

 These then multiply in the intervals between milking and some 

 types reach into the cistern, where they persist and from whence 

 they gradually invade upper parts of the udder. It may be 

 objected that the sphincter muscle at the teat is an obstacle to 

 the entrance of bacteria, but the folds of the muscle probably 

 leave openings of sufficient size to permit micro-organisms to pass. 



Whether this is the only source of bacteria in the udder re-^ 

 mains problematic. Harding and Wilson have observed that 

 during the first few days of the lactation period, the colostrum 

 period, germs were distinctly more abundant than later, and that 

 toward the end of lactation the numbers tended to decrease. 

 The authors suggest that perhaps the inflamed condition of the 

 udder during the early lactation period is responsible for the 

 large numbers of bacteria present, and that later, while the nor- 

 mal udder is in full flow, it is daily subjected to complete disten- 

 tion, which is the first stage of inflammation. And finally, when 

 the flow begins to fall off rapidly, the udder is no longer fully 

 distended, and this inflammatory condition ceases. The rela- 

 tion of the germ content of milk in the udder during inflammatory 

 conditions is a problem that has not been fully investigated, and 

 that may throw additional light on the presence of bacteria in 

 the udder. 



The number of bacteria in milk, when drawn aseptically from 

 the udder, varies in different animals and may also vary in the 

 qivarters of the udder of the same animal. Hastings and Hoff- 

 mann have studied the bacterial content in milk directly from the 

 udder of 3 cows, and found that the averages were 31,000; 191,000; 

 and 810 respectively. The authors think that the milk in the 

 udder of some cows contains consistently greater numbers of bac- 

 teria than in others, and that this fact should be taken into ac- 

 count when low bacterial numbers are specially desirable, as in 



