172 (il.NKUAL CHARACTERISTICS 



isolated his Micrococcus acidi lactis (which liquefies gelatin) from cheesy butter. 

 G. MARPMANN (I.) discovered five species belonging to this group in Gottingen 

 milk, and named them Bacterium lactis acidi, Bacillus lactis acidi, Bacterium 

 limhatum lactis ariJ/. Jficrococcus lactis acidi, and Sphcerococcus lactis aci<li. 

 G. GROTENFELT (II.) isolated a lactic-acid-forming, anaerobic Streptococcus acidi 

 lactici from Finnish milk. In his communication, issued from Hueppe's labora- 

 tory, there also occurs the remark that Bacillus acidi lactici II. can be perma- 

 nently deprived of its acidifying power by cultivating it for some time in media 

 free from sugar. This attenuation of the cultures is also often noticed in patho- 

 genic bacteria, many of which lose their virulence i.e. poisonous nature, and 

 consequent capacity of producing disease when kept for some time under 

 unaccustomed conditions of nutrition, viz., outside the animal body. Bearing 

 this in mind, Grotenfelt speaks of a variable virulence of Bacillus acidi lactici, 

 meaning thereby the possibility of reducing its fermentative power. 



The fermentative properties of the Bacterium lactis aerogenes, found by 

 ESCBERICH (I.) in the contents of the intestines of sucklings, and also in uncooked 

 cow's milk, were investigated by A. BAGINSKY (II.), who found that in artificial 

 media containing lactose it produces both acetic acid and lactic acid. The gas 

 liberated during the reaction consisted of CO 2 , 22 per cent.; H, 30 per cent.; 

 CH 4 , 9 per cent.; N, 39 per cent. R. WURTZ and R. LEUDET (I.) considered 

 this microbe to be identical with Pasteur's lactic acid bacillus, but their opinion 

 does not seem to be well founded. According to J. DENYS and J. MARTIN (I.), 

 B. lactis aerogenes is only a variety of the Pneumobacillus ( 33) discovered by 

 Friedlander. 



Respecting the Pediococcus acidi lactici discovered by P. LINDNER (I.) a few 

 particulars will be given in chapter xxv. ; and details concerning the part played 

 by the lactic acid bacteria in certain industrial fermentation processes, such as 

 distilling, dairying and cheese-making, tanning, &c., will be found in chapters 

 xxiii. to xxvii. 



136. The Equation of Lactic Fermentation 



is (when lactose or grape-sugar is presupposed as the raw material) generally 

 expressed in chemical text-books as follows : 



C^H^On + H 2 = 4^3^03 



Lactose. Lactic Acid. 



C 6 H ]2 6 = 2C 3 H 6 



3 . 



Actually the process is not so simple as here represented, a certain quantity 

 of the sugar employed being consumed by the organisms to enable them to dis- 

 charge their vital functions and bring about the fermentation in question. Con- 

 sequently the actual yield of lactic acid obtained is less than the theoretical 

 quantity calculated from the foregoing equations. Another proof of the complex 

 nature of the operation is afforded by the large quantity of gas liberated during 

 the fermentation, but which is not indicated in the reaction expressed by the 

 equations aforesuid. 



According to the researches of R. WARRINGTON (I.), the amount of acid pro- 

 duced varies greatly in different species, and is so small with some that (as noted 

 by Conn) it is insufficient to curdle the milk. This difference is explicable by 

 the varying susceptibility of the individual species to the adverse influence of 

 the resulting acid. On this account alone, fermentation may come to a stand- 

 still notwithstanding the presence of sufficient unconsumed nutrient material. 

 The difficulty is easily met by opportunely neutralising the acid by an addition of 



