YEAST 423 



Investigation subsequently has confirmed this original idea. 

 It has been shown that if you take any measures by which 

 other plants of like kind to the torula would be killed, and 

 by which the yeast plant is killed, then the yeast loses its 

 efficiency. But a capital experiment upon this subject was 

 made by a very distinguished man, Helmholz, who performed 

 an experiment of this kind. He had two vessels one of them 

 we will suppose full of yeast, but over the bottom of it, as 

 this might be, was tied a thin film of bladder ; consequently, 

 through that thin film of bladder all the liquid parts of the 

 yeast would go, but the solid parts would be stopped behind ; 

 the torula would be stopped, the liquid parts of the yeast 

 would go. And then he took another vessel containing 

 a fermentable solution of sugar, and he put one inside the 

 other ; and in this way you see the fluid parts of the yeast 

 were able to pass through with the utmost ease into the 

 sugar, but the solid parts could not get through at all. And 

 he judged thus : if the fluid parts are those which excite 

 fermentation, then, inasmuch as these are stopped, the sugar 

 will not ferment ; and the sugar did not ferment, showing 

 quite clearly, that an immediate contact with the solid, 

 living torula was absolutely necessary to excite this process 

 of splitting up of the sugar. This experiment was quite 

 conclusive as to this particular point, and has had very great 

 fruits in other directions. 



Well, then, the yeast plant being essential to the produc- 

 tion of fermentation, where does the yeast plant come from ? 

 Here, again, was another great problem opened up, for, 

 as I said at starting, you have, under ordinary circumstances 

 in warm weather, merely to expose some fluid containing 

 a solution of sugar, or any form of syrup or vegetable juice 

 to the air, in order, after a comparatively short time, to see 

 all these phenomena of fermentation. Of course the first 

 obvious suggestion is, that the torula has been generated 

 within the fluid. In fact, it seems at first quite absurd to 

 entertain any other conviction ; but that belief would most 

 assuredly be an erroneous one. 



Towards the beginning of this century, in the vigorous 

 times of the old French wars, there was a Monsieur Appert, 

 who had his attention directed to the preservation of things 

 that ordinarily perish, such as meats and vegetables, and 

 in fact he laid the foundation of our modern method of pre- 

 serving meats ; and he found that if he boiled any of these 

 substances and then tied them so as to exclude the air, that 



