BIOLOGY OF LACTIC ACID BACTERIA 273 



sterilization previous to use. Milk sterilized in the autoclave 

 acquires a brownish tinge, indicative of a change of state, which 

 makes it unfit for the demonstration of the proteolytic activities 

 of the lactic acid bacteria. For such a study milk should be 

 utilized that has been sterilized at a moderate heat so that its 

 white color has been preserved. By using this white-sterile milk 

 I was in a position to detect casein cleaving properties in some of 

 the lactic acid bacteria which in brown-sterile milk failed to 

 digest this compound. Some of the so-called propionic acid 

 bacteria behaved similarly. 



Undoubtedly, in this factor of appropriate sterilization is to be 

 found the reason why many authors claim for the lactic acid 

 bacteria negative or only neghgible casein-acido-dissolving prop- 

 erties, and therefore contrary to my opinion have ascribed to 

 them no role in the ripening of cheese. 



BACTERIAL FLORA OF THE UDDER 



The importance which the acid forming organisms seem to 

 bear, both from the standpoint of hygiene and in the dairy, gave 

 me occasion for a deep study. It is to be emphasized neverthe- 

 less that investigations seem to point to the fact that from the 

 hygienic and sanitary standpoint it is not only the cleanUness of 

 the stable and of the cow that are to be considered, but also other 

 internal and external factors. A fact of great importance in this 

 connection is, that apparently sound cows may harbor in their 

 udder for longer or shorter periods of time bacteria (cocci as well 

 as bacilli) which sometimes prove beneficial and other times 

 noxious both from the hygienic as well as from the dairying stand- 

 point. Therefore a selection of milch cows on the basis of this 

 udder flora has been proved useful by me and to this I have given 

 new support by carrying out fermentation tests as a means of 

 judging of the quaUty of the milk, especially of such milk as is 

 used for direct consumption by children and invalids. 



HEAT RESISTANCE 



It is generally assumed that an exposure of one quarter of an 

 hour at 60° to 80°C. is sufficient to destroy the non-spore-forming 



JOURNAL OF BACTERIOLOGY, VOL. VII, NO. 2 



