6 ELEMENTARY BIOLOGY. [CHAP. 



prevent its growth and reproduction. The greater part of 

 the sugar is resolved into Carbonic anhydride and Alcohol, 

 the elements of which, taken together, 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 Torttto. 



This is the more probable as Torula 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 

 live in saccharine solutions which contain no free oxygen, 

 appearing, under these circumstances, to get. its oxygen from 

 the sugar. 



It has further been ascertained that Torula 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 Torula 

 approaches that of animals. 



LABORATORY WORK. 

 Sow some fresh baker's yeast in Pasteur's fluid 1 with 



1 Pasteur's fluid : 



Potassium Phosph 20 parts. 



Calcium Phosph i ,, 



Magnesium Sulphate " ,, 



Ammonium Tartrate 100 ,, 



("Cane Sugar 1500 ] 



Water 8^76 



ro,ooo parts. 



The sugar is to be omitted when Pasteur's fluid " without sugar" is 

 ordered. Pasteur himself used actual yeast ash ; the above constituents 

 give an imitation ash, which, with the ammonium salt and sugar, 

 answers all practical purposes. 



