YEAST. 579 



ules of which Leeuwenhoek speaks, though the constancy of their ar- 

 rangement in sixes existed only in the worthy Dutchman's imagination. 



It was very soon made out that these yeast organisms, to which 

 Turpin gave the name of Torula cerevislce, were more nearly allied to 

 the lower Fungi than to any thing else. Indeed, Turpin, and subse- 

 quently Berkeley and Hoffmann, believed that they had traced the de- 

 velopment of the Torula into the well-known and very common mould 

 the Penicillium glaucum. Other observers have not succeeded in 

 verifying these statements ; and my own observations lead me to believe 

 that, while the connection between Torula and the moulds is a very 

 close one, it is of a different nature from that which has been supposed. 

 I have never been able to trace the development of Torula into a true 

 mould ; but it is quite easy to prove that species of true mould, such 

 as Penicillium, when sown in an appropriate nidus, such as a solution 

 of tartrate of ammonia and yeast-ash, in water, with or without sugar, 

 give rise to Torulce, similar in all respects to T. cerevisice, except that 

 they are, on the average, smaller. Moreover, Bail has observed the 

 development of a Torula larger than T. cerevisim> from a 3fucor, a 

 mould allied to Penicillium. 



It follows, therefore, that the Torulce, or organisms of yeast, are 

 veritable plants; and conclusive experiments have proved that the 

 power which causes the rearrangement of the molecules of the sugar is 

 intimately connected with the life and growth of the plant. In fact, 

 whatever arrests the vital activity of the plant also prevents it from 

 exciting fermentation. 



Such being the facts with regard to the nature of yeast, and of the 

 changes which it effects on sugar, how are they to be accounted for ? 

 Before modern chemistry had come into existence, Stahl, stumbling, 

 with the stride of genius, upon the conception which lies at the bottom 

 of all modern views of the process, put forward the notion that the fer- 

 ment, being in a state of internal motion, communicated that motion 

 to the sugar, and thus caused its resolution into new substances. And 

 Lavoisier, as we have seen, adopts substantially the same view. But 

 Fabroiii, full of the then novel conception of acids and bases and 

 double decompositions, propounded the hypothesis that sugar is an 

 oxide with two bases and the ferment a carbonate with two bases ; 

 that the carbon of the ferment unites with the oxygen of the sugar, and 

 gives rise to carbonic acid ; while the sugar, uniting with the nitrogen 

 of the ferment, produces a new substance analogous to opium. This is 

 decomposed by distillation, and gives rise to alcohol. Next, in 1803, 

 Thenard propounded an hypothesis which partakes somewhat of the 

 nature of both Stahl's and Fabroni's views. " I do not believe with 

 Lavoisier," he says, " that all the carbonic acid formed proceeds from 

 the sugar. How, in that case, could we conceive the action of the fer- 

 ment on it ? I think that the first portions of the acid are due to a 

 combination of the carbon of the ferment with the oxygen of the sugar, 



