MILK 91 



All these sources add bacteria to the milk, the first probably 

 being responsible for the greatest contamination. 



3. Bacteria introduced from Milk Vessels. When imperfectly 

 cleaned these are a source of great bacterial contamination to the 

 milk. 



4. From Special Milk Apparatus. The commonest ap- 

 paratus used, not strictly appertaining to milking, is a milk- 

 strainer. It is an almost universal practice of the cow-keeper to 

 strain the milk, usually immediately after milking. If not kept 

 absolutely clean milk strainers may actually add bacteria to the 

 milk. 



Milk-coolers are sometimes a source of bacteria in milk. 

 They may be placed in dusty places so that the milk passing 

 over them, exposing as it does a large surface to the air, takes 

 up a good many bacteria. Also they may not be kept perfectly 

 clean, traces of milk being left in which bacteria multiply enor- 

 mously and are subsequently added to the milk. A third but 

 much less common way by which coolers may contaminate the 

 milk, is by being leaky, the water being added in small quantity 

 to the milk. 



In the same way milk-separators usually add bacteria to the 

 milk passing through them as estimated by numerical counts. 

 This increase is however largely apparent and due to the breaking 

 up of clumps of bacteria. 



5. Contamination in Transit. It is an extremely difficult 

 thing to measure the amount of bacterial contamination of milk 

 which takes place in its transit from cowshed to milk purveyor 

 or consumer. The increase in the number of bacteria added 

 from outside sources is obscured by the increase due to the 

 multiplication of the bacteria already in the milk. 



The addition of bacteria from outside in transit is probably 

 trivial compared with the bacterial additions at the cowshed and 

 in the consumer's house. 



6. Bacteria added on the Purveyor s or Consumer's Premises. 

 Obviously the number of bacteria added must vary enormously 

 with the condition of the premises and the cleanliness practised 

 upon the premises. 



