BACTEEIOLOGY OF MILK 451 



access from this source are usually chromogenic cocci or 

 spore-bearing bacilli. 



Bacteria from the Hands of the Milker. — ^Undoubtedly 

 bacteria may gain access to the milk from the hands of the 

 milker. Bacteria from this source are particularly objec- 

 tionable inasmuch as they are of human origin, and if the 

 individual is suffering from any disease, there is a possibil- 

 ity of inoculating the milk with the organisms capable of 

 causing this disease and thus spreading it through the milk. 

 Many instances of infection in this manner are on record. 

 Typhoid fever has been spread as a result of milkers being 

 carriers of the disease. Diphtheria and scarlet fever have 

 also been transmitted through milk. 



Bacteria from Milking Vessels. — Studies made by sev- 

 eral of the experiment stations in the United States have 

 shown that this is probably the most important source of 

 initial infection by bacteria. Unless all milk utensils are 

 thoroughly sterilized there is a tendency to add many bac- 

 teria to the milk. Milking machines in particular are dif- 

 ficult to keep clean; The tubes should be thoroughly steril- 

 ized if gross contamination by bacteria is to be avoided. 

 In the period elapsing between the time when the milk is 

 drawn from the animal until it is finally delivered to the 

 consumer, there may be numerous opportunities for con- 

 tamination by bacteria. 



The number of bacteria actually present in the milk at 

 the time it is delivered to the consumer will vary according 

 to the relative importance of several factors. In the first 

 place, the number of bacteria gaining access to the milk 

 during the process of milking will be important. Milk that 

 is kept at a low temperature will allow but slow multiplication 

 of microorganisms. Milk kept at a higher temperature or 

 room temperature will show very rapid increase in bacteria 

 present. The temperature, then, at which milk is held, has 

 very important bearing upon the total number present 



