IX.] YEAST. 383 



it appears that the conditions which are most favourable to 

 the growth and multiplication of the Torula are unfavourable 

 to the process of fermentation. Thus the latter goes on 

 most vigorously in the absence of free oxygen, while its 

 presence is favourable to the increase of the yeast-cells. 

 The greater part of the sugar is resolved into Carbonic 

 anhydride and Alcohol, the elements of which, taken to- 

 gether, equal in weight those of the sugar. A small part 

 (4 — 5 P er cent.) breaks up into Glycerine and Succinic acid, 

 and one or two per cent, is not yet accounted for, but is 

 perhaps assimilated by the Torula. 



This is the more probable as Torulce will grow and multiply 

 actively in a solution in which sugar and Ammonium Nitrate 

 replace the Ammonium Tartrate of the former solution, in 

 which case the carbon of the Protein, Cellulose and Fat 

 manufactured must be obtained from the sugar. Moreover, 

 though oxygen is essential to the life of the Torula, it can, 

 as already mentioned, live in saccharine solutions which 

 contain no free oxygen, appearing, under these circum- 

 stances, to carry on its life by the substitution of the ab- 

 normal catabolic process of fermentation for the normal 

 respiration. 



It has further been ascertained that Torulce flourish re- 

 markably in solutions in which sugar and pepsin replace 

 the Ammonium Tartrate. In this case, the nitrogen of their 

 protein compounds must be derived from the pepsin; and 

 it would seem that the mode of nutrition of such Torulce 

 approaches that of animals. 



