IX.] YEAST. 381 



Water (H^O). 



Sugar (C.^H^A.)- 



Ammonium Tartrate (C4H^(NHJPJ. 



Potassium Phosphate (KH^POJ. 



Calcium Phosphate (CagPgOg). 



Magnesium Sulphate (MgSOJ. 



In this fluid the Tonilce will grow and multiply, But it 

 will be observed that the fluid contains neither Protein nor 

 Cellulose, nor Fat, though it does contain the elements of 

 these bodies arranged in a diff'erent manner. It follows that 

 the Torula must absorb the various substances contained in 

 the water and arrange their elements anew, building them 

 up into the complex molecules of its own body. This is a 

 property peculiar to living things. 



If, on the other hand, some Torula cells be added to a 

 quantity of pure distilled water, it will be found not only 

 that no growth or multiplication of the cells takes place, but 

 that the amount of their protoplasm actually undergoes a 

 perceptible diminution. Hence we see that there are 

 processes going on in the cells which tend to diminish their 

 substance. 



The chemical changes going on in a living cell, such as 

 that of yeast, may conveniently be spoken of collectively as 

 its metabolism. Among these changes those which result in 

 the building up of more complex chemical bodies, and thus 

 in an increase of the organic substance of the cell, constitute 

 its constructive metabolism or anabolis7ft, while to those 

 which bring about a diminution of organic substance, with 

 evolution of simpler compounds, such as carbonic anhydride, 

 the term destructive metabolism or catabolism has been 

 applied. 



It must be pointed out that the anabolic processes of the 



