BACTERIOLOGY OF MILK 447 



other changes as well, such as sweet curdling, ropiness, 

 soapiness and discoloration by pigment. The stages 

 enumerated above will be discussed in order. 



Germicidal Stage. Usually milk contains some bac- 

 teria when drawn from the udder. Others rapidly find 

 their way into it from the milking utensils, from dust, dirt, 

 the milker, etc. Careful observation of the apparent num- 

 bers of bacteria present in this milk indicate that there is 

 a period of diminution. The numbers of bacteria show a 

 tendency to decrease rather than to increase. It has been 

 assumed, therefore, that freshly drawn milk has a certain 

 amount of germicidal power. Experimentally it may be 

 readily demonstrated that freshly drawn milk, when inoc- 

 ulated with considerable numbers of many different kinds 

 of bacteria, will show a decided diminution in the numbers 

 upon plating. This action continues for a longer period 

 when the milk is held at a low temperature and disappears 

 more quickly at a higher temperature. There has been a 

 considerable amount of argument in the scientific world as 

 to whether this so-called germicidal action really represents 

 the actual destruction of bacteria, or whether it simply 

 means the bacteria have clumped together or agglutinated 

 and upon plating the number of colonies is reduced, 

 although the actual number of bacteria may even have 

 increased. The evidence seems to indicate that there is some 

 actual decrease in the numbers of bacteria. Various kinds 

 of antibodies have been detected in milk, particularly bac- 

 teriolysins. Microscopic examination, furthermore, reveals 

 considerable numbers of white corpuscles or leucocytes. 

 These do not cease their activity for some time after the 

 milk is drawn and it is possible that they may continue 

 phagocytic action and destroy some microorganisms. This 

 germicidal action never leads to the complete sterilization 

 of the milk. It may be that the action is to a certain degree 

 specific, some species of bacteria being destroyed while 



