68 THE TYPES OF MILK BACTERIA. 



ago found that milk would not sour in the milk gland, even 

 if allowed to remain there for a long time, and if this bac- 

 terium were present it would be expected that the milk would 

 sour because the conditions in the duct are favorable for its 

 growth. Moreover, careful study of the bacteria in the milk 

 duct's, and of milk drawn with aseptic precautions have dem- 

 onstrated that this bacterium is not commonly a normal in- 

 habitant of the milk duct. A study of the external sources of 

 contamination has shown that this organism may probably 

 always be found upon the hair of the cow, upon the hay, in dust 

 on the floor, in the air of the stall ; but that it is not found in 

 the ordinary dirt of the stall, in water, or in the excretions 

 from the animal (44) . Its primary source in ordinary milk 

 appears to be the skin of the cow, from which it drops dur- 

 ing the milking, and perhaps it comes also from hay dust. 

 It is extremely probable that the organism must have some 

 other normal habitat. It cannot grow upon the skin of the 

 cow, which is hardly moist enough for proper bacteria 

 growth. Moreover, the bacteria that get into the milk show, 

 as we shall notice later, indications that they are not at first 

 in a condition for vigorous growth. Probably, therefore, 

 there is some other source in nature where these organisms 

 live naturally and .where they grow and multiply. What that 

 source is has not as yet, however, been determined, though 

 it is possibly the leaves of grass. 



Distribution. This species is very .widely distributed, al- 

 though it does not appear to be anywhere in very great 

 abundance. It has been found in milk from nearly every 

 state in the United Stales, and it is equally common in the 

 milk in the dairies of Europe. When milk drawn directly 

 from the cow is examined at once the numbers of this species 

 are very few. Indeed, if exceptional care is taken to pre- 

 vent external contamination during the milking they are so 

 few in the fresh milk that they can rarely be found by ordi- 

 nary bacteriological methods of study and are frequently 



