GROWTH AND THE AGING PROCESS 



961 



TABLE 4 



EMBRYONIC GROWTH OF THE CEREBRAL CORTEX OF THE GUINEA PIG 



(Flexner and Flexner 1950 a, b — recalculated) 



34-37 39 



Age {days) 

 -41 46-51 60- 

 Tertn. 



Adult 



Observed data 



Water — g/kg total tissue 

 Fat — g/kg total tissue 

 Protein — g/kg total tissue 



Tissue phases 



Extracellular fluid — g/kg tissue 

 Total cells (fat-free) — g/kg tissue 

 Nuclei* — g/kg tissue 

 Cell body cytoplasm* — g/kg tissue 

 Processes plus glia — g/kg tissue 



Cellular constituents 



Water — g/kg fat-free cells 



Protein — g/kg fat-free cells 



High energy P + — mM/kg cell water 



Other acid-soluble P — mA//kg cell water 



Sodium — mM/kg cell water 



Phospholipid P — mM/kg fat-free cells 



Nucleic acid P — mM/kg fat-free cells 



* From histological measurements. 



+ From phosphocreatine, adenosine triphosphate, and adenosine diphosphate. 



In order that the picture seen in muscle tissue should not be considered as pos- 

 sibly exceptional and specific for that type of tissue, we may cite in more detail the 

 findings of Yannet and Darrow (1938) on postnatal changes in the liver. With 

 corrections made for fat, no significant change was seen in the concentration of 

 water in the hepatic cells in older as compared with younger cats. The livers of 

 the group of older animals did show a 12 per cent average decrease in extracellular 

 fluid. 



These authors also found a 12 per cent decrease in extracellular fluid in the 

 brains of the older group. Their calculations indicated that the water content of 

 the brain cells remains essentially constant. 



Detailed studies by Flexner and Flexner (1949, 1950a, 1950b) and by Peters 

 and Flexner ( 1 950) on the fetal development of the cerebral cortex of the guinea pig 

 show that extracellular fluid, again calculated from chloride, rises slightly at an 

 early period, when the spaces between the nerve cells are becoming wider, and 

 then undergoes a marked fall of about 50 per cent by the time that the adult stage 

 is reached (Table 4). 



We see, then, that the opinion that cells during the growth of the body are 

 undergoing a progressive dehydration is not supported by the data obtained in a 



Literature p. gyi 



