158 0. A. WATKINS ON YEAST AND OTHER FERMENTS. 



This unfolding under the action of Ferments is totally different 

 to that chemical change known as Catalysis, which takes place in 

 one substance by mere contact with another, such as the unfolding 

 of Alcohol into Ether, and Water, by contact with Sulphuric Acid ; 

 for although the acid causes such a wonderful change, it is not 

 destroyed by the operation, and, consequently, when once the pro- 

 cess is set going an unlimited quantity of alcohol may be converted 

 by the original acid. 



All the Ferments are highly complex azotised substances allied to 

 Albumen ; but while they possess this character in common, they 

 may be divided into two groups — the one being living organisms, 

 as Yeast, and the other substances derived from various organic 

 sources, such as Albumen, Gluten, Casein, Diastase, Emulsin, and 

 a variety of others — all of which decay most rapidly when in a 

 moist state. 



The authors of the " Microscopical Dictionary" would "exclude 

 these substances from the Ferments, and desire that the term 

 Fermentation be restricted to those changes which take place only 

 through the agency of living organisms or Fungi ;" regarding 

 which, they also, say, *' A general law appears to prevail through- 

 out the Fungi that their nutrition differs from that of all other 

 plants in depending exclusively on the absorption and decomposition 

 (with the evolution of carbonic acid gas) of organic compounds, 

 therefore consisting of the performance of the operation of 

 fermentatation on the organic matters on which they feed." 

 But as the chemical operations of the Ferments are so similar, 

 notwithstanding the wide difference in their organisation, I consider 

 there would be no advantage in separating them as proposed, as 

 they form a distinct class of chemical phenomena. I have also to 

 observe that it is not true that carbonic acid gas is always given off 

 during fermentation, nor is it proved that it is evolved during the 

 growth of all the Fungi. The Ferments to which I desire to call 

 your attention are — 



Mycoderma Vini, or Yeast, which converts Sugar into Alcohol. 

 Boiled Yeast, which converts Sugar into Gum and Mannite — 



this transformation being called the Viscous Fermentation. 

 Casein, which converts Sugar into Lactic Acid and Butyric 



Acid ; this last conversion, however, being attributed to 



the action of the Vibrio and Diastase, which converts 



starch into sugar. 



