312 DISTRIBUTION OF BACTERIA 



This fermentation is undesirable in that it produces a taste 

 which is objectionable to most people and produces a physical 

 change in the milk which is ordinarily objectionable. Methods 

 of preservation are aimed almost entirely against this fermen- 

 tation. This does not mean of course that the fermentation 

 of milk by the lactic acid bacteria produces a harmful change 

 in milk. MetchnikofT has called attention to the fact that the 

 Bulgarians make use of sour milk as a beverage, and he sug- 

 gests that lactic acid organisms may serve a very useful pur- 

 pose in the intestines of man since they antagonize the putre- 

 factive bacteria which have a very undesirable influence on 

 health by forming metabolic products that are detrimental. 

 In the production of butter, at least in this country, we are 

 dependent upon the fermentations caused by these bacteria. 

 One of the great problems, then, of the dairyman is the pro- 

 duction of a milk in which the lactic acid fermentation is held 

 in check for a reasonable length of time; and it is possible, 

 with the greatest care, to produce a milk which will remain 

 sweet for many days. 



Slimy Milk. Slimy milk may be produced as the result of 

 bacterial growth. Some bacteria grow in milk, and secrete a 

 mucilaginous substance which causes the milk to assume a 

 slimy character. Sometimes this slime causes long strings or 

 ropes to appear in the milk. This is an undesirable fermenta- 

 tion, although not dangerous to health. Very frequently it 

 may be carried from one farm to another through the creamery 

 or cheese factory products; that is, through the skim milk or 



