20 GENERAL CONDITIONS AFFECTING BACTERIA IN MILK 



it is possible to draw from the udder of a healthy cow perfectly 

 sterile milk, which retains its sterility unchanged for long periods 

 of time in a sterilised and sealed flask. Yet we know by 

 practical experience as well as by ultimate changes in the milk 

 that, generally speaking, the presence therein of bacteria is very 

 marked. We must therefore next consider whence comes this 

 pollution. 



The Sources of Bacteria in Milk 



These are various and depend upon many minor circumstances 

 and conditions. 



For all practical purposes there are four chief opportunities 

 between the cow and the consumer when milk may become 

 contaminated with bacteria : — 



1. At the time of milking. 



2. During treatment and preparation, 



3. During transit to the town or dairy or consumer. 



4. After arrival at its destination. 



The following table, compiled from the experiments of 

 Backhaus of Konigsberg, will show the possible sources of con- 

 tamination at a glance : — 



