I.J YEAST. 3 



which readily diffuse themselves through the snrroundiDg- 

 fluid. The whole structure is called a 'cell;' the sac being 

 the 'cell- wall' and the contents the 'protoplasm.' 



When yeast is dried and burned in the open air it gives 

 rise to the same kind of smell as burning animal matter, and 

 a certain quantity of mineral ash is left behind. Analysed 

 into its chemical elements, yeast is found to contain Carbon, 

 Hydrogen, Oxygen,Nitrogen, Sulphur, Phosphorus, Potassium, 

 Magnesium and Calcium ; the last four in very small quanti- 

 ties. 



These elements are combined in different ways, so as 

 to form the chief proximate constituents of the Torula, which 

 are (1) a Protein compound, analogous to Casein, (2) Cellulose, 

 (3) Fat, and (4) Water. The cell- wall contains all the Cellulose 

 and a small proportion of the mineral matters. The protoplasm 

 contains the Protein compound and the Fat with the larger 

 proportion of the mineral salts. 



These Torulm are the 'particles' in the yeast which have 

 the power of provoking fermentation in sugar ; it is they 

 which are filtered off from the yeast when it loses its effi- 

 ciency by being strained through porous earthenware ; it 

 is they which form the fine powder to which yeast is reduced 

 by drying, and which, from their extreme minuteness, are 

 readily diffused through the air in the form of invisible 

 dust. 



That the Torulce are living bodies is proved by the 

 manner in which they grow and multiply. If a small 

 quantity of yeast is added to a large quantity of clear 

 saccharine fluid so as hardly to disturb its transparency, 

 and the whole is kept in a warm place, it will gradually 

 become more and more turbid, and, after a time, a scum of 

 yeast will collect, which may be many thousand, or million, 

 times greater in weight than that which was originally 

 added. If the Torulm are examined as this process of 



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