198 BUTYRIC ACID FERMENTATION. 



alkaline, water (free from bacteria), are exposed to the action of 

 pure cultures of this bacillus, they quickly lose the greater portion 

 of their pectin content, the loss of weight they suffer being almost 

 exclusively due to this cause. As reported by E. PFUHL (II.), a 

 patent has been obtained in the United States by Allison and 

 Pennington for the method tested by them, whereby the retting 

 of flax can be effected in a few days in any class of water, by the 

 addition of salts promoting the growth of the desired ferment. 

 Perhaps an inoculation by water from a locality such as the 

 river Lys, a tributary of the Schelde where flax-retting is exten- 

 sively carried on, is also to be made. 



120. The Rancidity of Fats, particularly Butter, 



will be briefly dealt with here parenthetically, as there is no other 

 appropriate place for it. The characteristic indication of this well- 

 known phenomenon is an increase in the percentage of free acids 

 (chiefly the volatile acids, butyric, caproic, &c.). This may be 

 attributed to four different causes : (i.) The activity of lactic acid 

 bacteria converting the residual lactose in the butter into lactic 

 acid, which latter is then transformed into butyric acid by Granu- 

 lobater lactobutyricum ; (2.) The decomposition of albuminoids 

 (casein) by bacteria capable of forming butyric acid therefrom \ 

 (3 and 4.) The dissociation of the fats into glycerin and free 

 fatty acids, either by bacterial agency on the one hand, or by the 

 action of light and air on the other. The preponderance of one 

 or other of these causes depends on the attendant circumstances. 



E. DUCLAUX (VI.) rendered valuable service in demonstrating 

 the influence of air on the fatty matter of butter and cheese, and 

 by showing that this influence is twofold, viz., it first, by saponi- 

 fication, breaks the matter up into glycerin and fatty acids, and 

 then converts the latter, (especially oleic acid) into oxy compounds. 

 In the dark, and in presence of a copious supply of air, saponifica- 

 tion predominates, the butter then smelling strongly of butyric 

 acid ; but 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 neces- 

 sarily 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 ques- 

 tion 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 condi- 

 tions, 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 



