PROTOPLASM 41 



the chemical transformation of the protoplasm." Granules of " volutin " 

 formed in the cytoplasm are also looked upon as a food substance used 

 by the nucleus in the elaboration of chromatin. 



The fatty components of the cel^ comprise both ordinary fats and 

 lipoids (fat-like bodies not decomposed by alkalis); among the latter 

 lecithin and cholesterin are of great importance, particularly in the cells 

 of animals. 



The carbohydrates found in protoplasm are chiefly pentoses and 

 hexoses, which are as a rule combined with proteins and with lipoids. 

 Glycogen exists free in the cells of many tissues and serves as a source of 

 heat and energy. The important role played by pentosans in the activity 

 of the plant cell is strongly emphasized by Spoehr (1919) and Macdougal 

 (1920); in fact these authors speak of protoplasm as "an intermeshed 

 pentosan-protein colloid." 



Inorganic salts are present in considerable variety, as shown by the 

 presence of the following elements in the ash of Fuligo protoplasm: Cl, 

 S, P, K, Mg, Na, Ca, Fe. 



Because of their failure to find any new types of chemical compounds 

 in their analysis of protoplasm Reinke and Rodewald (1881) thought it 

 probable that the peculiarities of protoplasm are due to its structure 

 rather than to its chemical composition. It has since been found, how- 

 ever, that certain of the life processes continue for a time after the pro- 

 toplasm has been ground up mechanically. Moreover, more refined 

 analytical methods have enabled chemists to isolate from protoplasm 

 certain extremely complex and unstable proteins (the " protoplasmids " 

 of Etard), which differ greatly in degree of complexity, if not otherwise, 

 from proteins encountered elsewhere. 



Varieties of Protoplasm. From the foregoing resume it is plain that 

 in protoplasm, because of the many combinations possible among con- 

 stituents present in such great variety, we have a substance which may 

 exist in a vast number of different forms. When it is further recalled 

 that many of the constituents exhibit singly the phenomenon of stereo- 

 isomerism this number is seen to be incalculable. For example, it was 

 shown by Miescher that an albumin molecule with 40 carbon atoms 

 could have about one billion stereoisomers, and some albumins probably 

 have more than 700 carbon atoms. Albumin, moreover, is only one of 

 many complex substances present in protoplasm. Hence, the state- 

 ment that all living cells are composed of the same substance, proto- 

 plasm, is true only in a general sense. Although they are made up of 

 the same categories of substances existing in the same general type of 

 organization the hydrocolloidal state the protoplasms of different 

 organisms vary widely in the relative amounts of these leading con- 

 stituents. For example, the lipoids are much more abundant in the 

 protoplasm of animals than in that of plants, and the carbohydrate- 



