iv.] YEAST. 83 



and alcohol, which is not unjustly ridiculed in the most 

 surprising paper that ever made its appearance in a 

 grave scientific journal, 1 may be untenable, the fact that 

 the TorulcB are alive, and that yeast does not excite fer- 

 mentation unless it contains living Tdrulcs, stands fast. 

 Moreover, of late years, the essential participation of 

 living organisms in fermentation other than the alco- 

 holic, has been clearly made out by Pasteur and other 

 chemists. 



However, it may be asked, is there any necessary op- 

 position between the so-called " vital " and the strictly 

 physico-chemical views of fermentation ? It is quite pos- 

 sible that the living Torula may excite fermentation in 

 sugar, because it constantly produces, as an essential part 

 of its vital manifestations, some substance which acts 

 upon the sugar, just as the synaptase acts upon the 

 amygdalin. Or it may be, that, without the formation 

 of any such special substance, the physical condition of 

 the living tissue of the yeast plant is sufficient to effect 

 that small disturbance of the equilibrium of the particles 

 of the sugar, which Lavoisier thought sufficient to effect 

 its decomposition. 



Platinum in a very fine state of division known as 

 platinum black, or noir de platine has the very singu- 

 lar property of causing alcohol to change into acetic acid 

 with great rapidity. The vinegar plant, which is closely 



1 " Das entra'thselte Geheimuiss der geistigen Gahrung (Vorlaufige briefliche 

 Mittlieilung) " is the title of an anonymous contribution to Wohler and 

 Liebig's " Aunalen der Pharniacie" for 1839, in which a somewhat Rabelaisian 

 imaginary description of the organization of the " yeast animals " and of the 

 manner in which their functions are performed, is given with a circumstantiality 

 worthy of the author of Gulliver's Travels. As a specimen of the writer's humour, 

 his account of what happens when fermentation comes to an end may suffice. 

 " Sobald namlich die Thiere keinen Zucker mehr vorfinden, so fressen sie sich 

 gegeuseitig selbst auf, was durch eine eigene Manipulation geschieht ; alles wird 

 verdaut bis auf die Eier, welche unverandert durch den Darmkanal heneinehen ; 

 man hat zuletzt wieder gahrungs-fahige Hefe, namlich den Saamen der Thiere, 

 der iibrig bleibt." 



Or 2 



