THE RANCIDITY OF FATS 153 



fication predominates, the butter then smelling strongly of butyric acid ; bub if, 

 on the contrary, the oxidising action gets the upper hand, then a tallowy flavour 

 is the result. 



A recognition of the influence of light and air does not necessarily imply that 

 bacteria play no active part in rancidity. This latter view was maintained by 

 H. SCHULZ (II.) in 1878, but was afterwards denied by E. RITSERT (I.), ARATA (I.), 

 and others. With reference to the careful work performed by Ritsert, it should 

 be remarked that the main point is in the treatment of the question as to the 

 occurrence of rancidity in the absence of micro-organisms. The affirmative 

 answer thereto does not, however, involve the conclusion that their activity is, 

 under natural conditions, unimportant for the development of rancidity. The 

 action of the lactic acid bacteria can be illustrated by a practical example 

 afforded by the so-called Paris butter. This is a particularly stable product, and 

 is prepared from sweet cream, which, before churning, is heated to nearly 100 C. 

 and then rapidly cooled again, whereby the fission fungi just mentioned are 

 killed. The bacteria which split up the glycerides in butter include one which 

 R. KRUEGER (I.) isolated from butter that had become cheesy, and which he 

 named Bacillus Jtuorescens non liquefaciens. 



Investigations on the breaking up of fats by bacteria, which process is of 

 medic il interest in connection with the putrefaction of dead animals, were con- 

 ducted by G. vos SOMMARUGA (I.), chiefly with pathogenic species, only a few of 

 which were found to possess this power. Among these may be mentioned 

 Bacillus typhi abdominal-is, B. pyocyaneus, Micrococcus tetragenus, Vibrio cholerce 

 asiaticce, Deneckes spirillum, and others. On the other hand, Bacillus mega- 

 therium and B. subtilis do not possess it. 



