116 CYTOCHEMISTRY OF PROTEINS 



the nuclear membrane, but the concentration diminishes farther 

 away from the nuclear membrane. 



From these observations Caspersson concluded that "the 

 nucleic acids take part in the synthesis of cellular proteins, not 

 only in the nucleus but also in the cytoplasm." 



Caspersson's Chemical System 



Corresponding to the pattern of behaviour and composition of 

 the various cell organs just outlined, a scheme of chemical or- 

 ganisation is postulated. The scheme may be summarised under 

 four headings: 



1. Nucleic acids participate in an essential manner in the formation of 

 both nuclear and cytoplasmic proteins. 



2. In the reproduction of the gene protein, the participating nucleic acids 

 are of the deoxypentose type. 



3. In the formation of the cytoplasmic proteins, the participating nucleic 

 acids are of the pentose type. 



4. The nucleolus-associated chromatin (or heterochromatin) governs the 

 level of nucleic acid formation, and consequently also determines the rate 

 of protein production. 



These four postulates all derive ultimately from the experi- 

 mentally observed correlation between protein synthesis and the 

 existence of a high concentration of nucleic acids within the same 

 cell. This correlation is quite adequately established. But, on 

 the other hand, there are other ingredients in these four postu- 

 lates which are not so well established and need more critical 

 examination. To conduct this examination, and to obtain more 

 precise information about the manner in which nucleic acids 

 control protein production, we can profitably consider a number 

 of studies made by other than cytochemical methods. But be- 

 fore doing so it is desirable to consider briefly the nature of the 

 systems in which the nucleic acid-protein synthesis has been se- 

 curely established. 



Systems Displaying Protein Synthesis and High Nucleic 

 Acid Concentrations 

 A very interesting system to study from this point of view is 

 the growing oocyte and its attendant nurse cells, and the subse- 

 quent development of the fertilised ovum. In the formation of 

 the oocyte a great increase in cytoplasmic protein occurs with 



