OF NUTRITION; OR, WHY WE GROW. 51 



body are carried on : that decomposition not only 

 creates the necessity, but at the same time furnishes 

 the force of recomposition." 



The phenomena of fermentation afford a test of 

 the soundness of this conception. Vegetable juices 

 during fermentation undergo a process of slow 

 decomposition. If, during this process, certain 

 peculiar germs are present, a plant consisting of 

 cells, and low in the scale of vegetable life, is 

 developed. This plant is what we call the Yeast 

 Now, if the force given out by the liquid in 

 fermenting be the cause of the growth of the plant, 

 yeast should never be formed unless fermentation 

 is going on. If, on the other hand, the growth of 

 the plant be (as has been supposed by some) the 

 cause of the decomposition, then fermentation should 

 never occur unless that growth takes place. But 

 it is well known that the yeast plant is never 

 developed except during fermentation, while fermen- 

 tation will take place, although more slowly, without 

 any formation of yeast. It follows, therefore, that 

 the growth depends upon the decomposition, and 

 not the decomposition upon the growth. 



42 



