IX.] YEAST. 2^3 



it appears that the conditions which are most favourable to 

 the growth and multiphcation of the Toi'ida 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 

 breaks up into Glycerine and Succinic acid, and one or two 

 per cent, is not yet accounted for, but is perhaps assimilated 

 by the Toridce. 



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 Tonila, 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 lias further been ascertained that Tonihc 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 To)'ulce 

 approaches that of animals. 



