28 Living and Dead Matter and 



may also refer to experiments of Robertson with pepsin 

 on the products of caseinogen to which we shall return 

 in the next chapter. It therefore looks at present as 

 if van't Hoff's idea of reversible enzyme action might 

 hold in the modification offered by Armstrong. It 

 remains doubtful, however, whether this reversibility 

 can explain all the synthetic processes in the cell. No 

 objection can be offered at present if any one makes 

 the assumption that each cell has specific synthetic 

 enzymes or some other synthetic mechanisms which 

 are still unknown. 



The mechanisms for the synthesis of proteins must 

 have one other peculiarity: they must be specific in 

 their action. We shall see in the next chapter that 

 each species seems to possess one or more proteins not 

 found in any other but closely related species. Each 

 organism develops from a tiny microscopic germ and 

 grows by synthetizing the non-specific building stones 

 (amino acids) into the specific proteins of the species. 

 This must be the work of the yet unknown synthetic 

 enzymes or mechanisms. The elucidation of their 

 character would seem one of the main problems of 

 biology. Needless to say crystallography is not con- 

 fronted with problems of such a nature. 



The fact that the living cell grows after taking up 

 food has given rise to curious misunderstandings. 

 Traube has shown that drops of a liquid surrounded 

 with a semipermeable membrane may increase in 



