58 Dairy Bacteriology. 



simply racial differences exist in many cases, and there- 

 fore, that they are not distinct species. 



As a rule this class of bacteria is unable to liquefy 

 gelatin or develop spores. On account of this latter 

 characteristic they are easily destroyed when milk is pas- 

 teurized or heated to a higher temperature. They live un- 

 der aerobic or anaerobic conditions, many of them being 

 able to grow in either environment. According to Hoft 1 

 spontaneous souring occurs more rapidly in vessels hav- 

 ing a small surface exposed to the air, indicating that 

 anaerobic activity was more pronounced. 



The temperature conditions as to growth vary some- 

 what with different species. With most species growth 

 occurs at 50 F., but appreciable amounts of acid are not 

 produced until a higher temperature is reached 2 . 



While the souring of milk is a very wide- spread phe- 

 nomenon, still lactic acid germs do not abound every- 

 where. Esten finds them abundantly in the milk- ducts 

 but not present on hay. From the milk dealer's stand- 

 point, this fermentation like all others, is undesirable, as 

 it destroys the food value of milk for direct consump- 

 tion. The fermented product, sour milk, has some value 

 for cooking purposes. From this fermented product, 

 the Armenians make a palatable drink, matzoon, that 

 has considerable dietetic value in certain stomach 

 troubles. 



While these bacteria are undesirable in milk- supplies, 

 they are essential to the production of butter and cheese. 

 The aroma and flavor of butter is, as a rule, dependent 

 upon their presence, and in cheese they are absolutely 

 essential in various stages of its manufacture. 



Milch Ztg., 26: 212, 1897. 

 2 Kayser, Cent. f. Bakt., II. Abt., I: 436. 



