I CYTOPLASM 179 



Interrelation of the particulate globules and the reticulate ground-cytoplasm. 

 While it is fairly well established that the submicroscopic reticulate 

 structure of the cytoplasm is formed by linear aggregation or by 

 reversible denaturation of globular protein molecules, there is no 

 proof that all existing submicroscopic protein particles participate in 

 these sol- gel transformations. It is possible that certain globules, 

 as, e.g., the microsomes in the liver, may be specialized for metabolic 

 work, whereas others with the capacity of forming gels have the 

 character of structural proteins. It seems unlikely that the two funda- 

 mental tasks of the cytoplasm, metabolism and morphogenesis, are 

 performed by the same globular elements. It is true that some investi- 

 gators think of a uniform type of cytoplasm; thus Virtanen (1948) 

 finds that the number of enzymes in bacteria is so high, that all protein 

 molecules in the cytoplasm must be enzymes. On the other hand, we 

 find that in the microscopic domain individuaUzed and mobile meta- 

 bolic centres, such as erythrocytes or chloroplasts, are suspended in 

 a liquid which can gelate (fibrinogen- fibrin transformation, sol-gel 

 transformation of the endoplasm). Similar specialization might there- 

 fore conceivably prevail in the submicroscopic domain. 



We may note here that pieces of cytoplasm separated from the rest 

 continue to live independently, although they are not capable of 

 restoring the original cell shape. Thus, since metabolism is confined 

 to quite specific molecular configurations, all essential groupings have 

 to occur repeatedly in each cytoplast ; this is the case if they are 

 carried by submicroscopic particles. 



The development of the organism is presumably also governed by 

 special specific groupings in the cytoplasm, which can be designated 

 as morphogenetic configurations. However, in contradistinction to the 

 majority of active groups regulating the metabolic process, these 

 configurations do not by any means occur in every type of cell ; they 

 are confined to the cells of certain tissues, probably located in the 

 nuclei. A tissue of this kind acts as "organizer" (Spemann, 1936; 

 Weiss, 1939; Baltzer, 1942), since the processes of development 

 concerned can only take place in its presence. This organizer can be 

 influenced by chemical means. Lehmann (1937a, b), for instance, has 

 succeeded in controlling chorda formation by treating the gastrula of 

 Triton or Rana with lithium chloride. This can be explained by as- 

 suming that the essential morphogenetic configuration is changed 



