1 



BACTERIAL CONTAMINATION OF NORMAL MILK. 39 







number of bacteria which are found in the fore milk is prac- 

 tically the same as it is if the milking occurs at intervals as 

 long as two days, a fact which seems to indicate that the 

 bacteria develop to a certain extent and then are checked in 

 their growth by some unknown cause. 



It is also an interesting fact that not all bacteria not even 

 normal milk bacteria are capable of finding a habitat and 

 growing within the milk ducts. Experiments have been 

 made of injecting bacteria into the milk ducts and then test- 

 ing the milk drawn upon the following days (31). The 

 results show that the bacteria that have been used are 

 not able to colonize in the milk ducts. For a few days 

 after injection they are present in some abundance, but 

 they soon become reduced in numbers and finally disappear. 

 In these experiments the bacteria that have been used for 

 inoculation are not those which are commonly found in the 

 milk ducts but are in some cases unusual forms like B. pro- 

 digiosus. In one case, however, the ordinary lactic bacteria 

 found in milk have been used, but even these did not succeed 

 in living long, a result which is not surprising in view of the 

 fact that these bacteria are not commonly found in the milk 

 ducts. 



The species of bacteria which are found living in the ducts 

 are somewhat variable. There do not appear to be a very 

 large number of species normally inhabitating the duct, and 

 the variety which is found, even in fore milk, is small com- 

 pared to the variety of species found in milk shortly after 

 the milking. The species which are found in the milk ducts 

 are different with different cows, but apparently, in most 

 cases, there may be found within these ducts certain species 

 of streptococci. If the milk gland is the seat of an inflam- 

 matory process due to any of the pus-forming cocci the 

 bacteria present in the milk at the beginning of milking will 

 be the pus-forming streptococci. But the normal milk from 

 the healthy gland is almost sure to show the presence of 



