86 



FERMENTS AND MICRO-PARASITES. 



4. Ferment- 

 by so-called 

 ferment? 



ments with any unknown kind of micro-organisni that 

 no species is able to cause the putrefactive decomposition 

 of albumen. 



4. More weighty objections, which have held their 

 ground up to the most recent times, were brought 

 forward by those investigators who sought a more 

 directly chemical explanation of the processes of fer- 

 mentation, and did not regard the vitalistic theory as 

 clearing up, but on the contrary as obscuring what it 

 was desired to unravel. Liebig, more especially, and at 

 a later date Hoppe-Seyler took part in this opposition ; 

 Colin, Billroth, Hiller, Fleck, and others joined them. 



As early as the year 1839 Liebig had endeavoured to 

 explain the phenomena of fermentation and putrefaction 

 by assuming the existence in yeast of a soluble proteid 

 substance, which in breaking up excited the decompo- 

 sition of the sugar exactly in the same way as numerous 

 well-known chemical bodies when uniting or breaking 

 up are able to excite a similar movement of the atoms 

 in other bodies. This breaking up of the soluble 

 proteid substances is not an act of the living yeast 

 cells, but on the contrary is a correlative phenomenon 

 of their death. It is a peculiarity which may be 

 noticed in many chemical actions, that relatively small 

 quantities of the body which is breaking up are able to 

 set up the decomposition of large quantities of the other 

 body; thus Liebig instanced the decomposition of 

 oxalic acid, oxamid, and water in which a small quantity 

 of oxalic acid is sufficient for a large amount of oxamid ; 

 he also pointed out the similar fact in the decomposition 

 of cyanogen by aldehyde in the presence of water. The 

 difference between the alcoholic fermentation and the 

 putrefactive process can be easily explained on Liebig's 

 view. In putrefaction the decomposition is transmitted 

 by the decomposing albuminous material itself, so that 

 the process once begun continues by its own movement 

 even after the original cause which set it going has be- 

 come inactive ; in fermentation, on the other hand, the 

 sugar (the substance here undergoing decomposition) is 

 unable to transmit its own movement, and hence a 



