Fermentations in Milk. 65 



the Middle States. He found a germ in all but two cases 

 that agreed in general with Gunther's description. Din- 

 widdie, 1 studying the same question in Arkansas, arrives 

 at the same conclusion. This preponderance of evidence 

 makes it quite probable that there is a widely distributed 

 germ that is concerned in this change although undoubt- 

 edly different varieties exist. Besides this widely dissemi- 

 nated type, there are numerous other forms 2 that are 

 associated with this type of decomposition the most promi- 

 nent of which is known as B. lactis aerogenes. Conn and 

 Aikman refer to the fact that over one hundred species 

 are already known. It is fair to presume, however, that 

 a careful comparative study of these would show that 

 simply racial differences exist in many cases, and therefore, 

 that they are not distinct species. 



This class of bacteria is characterized by their inability 

 to liquefy gelatin or develop spores. On account of this 

 latter characteristic they are easily destroyed when milk is 

 pasteurized. They live under aerobic or anaerobic condi- 

 tions, many of them being able to grow in either environ- 

 ment, although, according to McDonnell, 3 they are more 

 virulent when air is not excluded. 



The- temperature conditions as to growth vary somewhat 

 with different species. With most species this occurs at 

 50 F., but appreciable amounts of acid are not produced 

 until a higher temperature is reached. 4 The optimum 

 temperatures for growth range from 90-95 F. 



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

 enon, still lactic acid organisms are not universal^ dis- 



1 Bull. 45, Ark. Expt. Stat., May 1897; Leichmann, Hyg. Rund., 1899, p. 1267. 



2 Kayser, Ann. de Tlnst Past., 10:737. 



3 McDonnell, Inaug. Diss., Kiel, 1899, p. 39. 

 * Kayser, Cent. f. Bakt., II Abt. 1:436. 



5 



