DEFENSIVE FERMENTS OF THE ANIMAL ORGANISM 7 



deeper insight into the working of the metabolic 

 processes of the cells, and obtain important clues as 

 to the means by which the cells of the animal organ- 

 ism produce, from compounds of a definite kind, 

 substances that belong to a different group. We 

 may mention here, for instance, the conversion of 

 amino-acids into grape sugar, and of carbohydrates 

 into fats. 



Some of the unicellular forms of life, and some 

 organisms consisting of a few groups of cells, are, at 

 least in part, equipped with agents (ferments) which 

 are not so precisely directed against certain substrates 

 "as the ferments of the higher species, such as plants 

 and animals. While the ferments of the latter, so 

 far as we know, principally decompose substrates 

 consisting of units which are found in the cell-con- 

 stituents that constantly recur in Nature, cases h'ave 

 been observed amongst the lower organisms (i.e., 

 morphologically lower) where the latter split up 

 compounds, which have been prepared in the labora- 

 tory from units which are not known to exist in a 

 free state in Nature. Owing to this wider indepen- 

 dence these organisms are assured of better conditions 

 of existence. These cells can live where others, being 

 unable to secure the energic contents of the material 

 supplied to them, and being also unable to form from 

 this substrate the elements required for their bodies, 

 are bound to perish through lack of nourishment. In 



