2O8 AGRICULTURAL BACTERIOLOGY. 



the yeasts to produce alcohol. The lactic fermentation occurs 

 simultaneously, producing more or less of a curdling. Kefir is 

 a beverage originating in the Caucasus mountains and is now 

 distributed somewhat widely. It never occurs in the dairy and 



FIG. 28. 



A large-sized kefir grain and the three species of bacteria of which it is composed. ( Freudenreich.) 



has no special significance in dairying. Although alcoholic 

 milks are of some dietetic value and of considerable commercial 

 interest, we need not consider them further. 



SUMMARY. 



From the facts outlined we may make the following sum- 

 mary : Although milk, when secreted from the milk gland, 

 is sterile, it is sure to become contaminated with bacteria while 

 being drawn into the milk pail. The chief sources of these 

 bacteria are the milk ducts, the outside of the cow and the 

 milk pail. The bacteria which are liable to get into the milk 

 are capable of producing a large variety of changes in it. 

 Ordinarily, some of the few varieties of lactic organisms 

 are pretty sure to get into the milk, and these find the milk 

 such a favorable medium for their growth that they increase 

 rapidly and soon develop lactic acid and cause the milk to 

 sour. They grow so rapidly as to leave all other species be- 



