54 PROTOPLASMIC ACTION AND NERVOUS ACTION 



rived from the oxidation of other compounds, especially 

 carbohydrates.^ 



It is especially signiiicant that in all cases the synthesis 

 of specific proteins, the reactions essential to growth 

 and maintenance, requires the intact protoplasmic 

 structure. These syntheses constitute the chemical 

 reactions most highly characteristic of the living state. 

 At one time it was believed that all of the metabolic 

 syntheses were the result of the special activity of 

 living protoplasm, and that the chemical reactions of 

 dead protoplasm or cell-extracts were always of a 

 catabolic (splitting) kind; it is now known, however, 

 that various syntheses involving little change of energy, 

 e.g., the synthesis of esters and disaccharides, readily 

 occur under the influence of enzymes alone. Yet the 

 fundamental fact remains that the more important or 

 specific part of the synthetic activity of protoplasm is 

 exhibited only during life. A relation of the normal 

 protoplasmic structure to certain types of chemical 

 action, especially synthetic action, is thus indicated. 

 With the alteration of structure occurring at death, as 

 indicated by loss of semi-permeability, coagulation of 

 cell-proteins, and other phenomena of disintegration, is 

 associated a loss of synthetic power. Only the living 

 yeast cell can build up from a solution of sugar, tartrates, 



^ Hence the importance of carbohydrates for growth and assimila- 

 tion; e.g., in plants, carbohydrate is indispensable for the assimilation 

 of amino-acids by yeast and molds (cf. the series of papers by F. Ehr- 

 lich, Biochem. Zeitschrifi, I, VIII, XVIII, XXXVI (1906-11); similarly 

 in higher plants the synthesis of proteins from amides in germination 

 requires the presence of carbohydrates (cf. Jost's Physiology of Plants, 

 p. 175, for a summary of the chief facts). The sequence of metabolic 

 derangements associated with diabetes shows the fundamental importance 

 of carbohydrate metabolism in higher animals. 



