g62 GROWTH AND THE AGING PROCESS I4 



TABLE 5 



CHANGES INDUCED BY ATROPHY IN THE GASTROCNEMIUS MUSCLE OF 



THE RAT 



(Hines and Knowlton, 1937) 



* Assuming extracellular phase originally contained 20 % solids. 



fairly large number of studies both on the whole organism and on various individ- 

 ual tissues. It seems, rather, that a decrease of extracellular fluid occurs and that 

 the water content of the protoplasm of the cells or, in the case of muscle, of the 

 syncytial fibers, remains essentially constant. The present concept is that the 

 decrease in extracellular fluid is due primarily to an increase in the proportion of 

 cells, e.g. of protoplasm, to the total mass of the tissue. These findings indicate 

 the need for studies on individual cells as by the methods of histochemistry, rather 

 than on masses of tissue, if conclusions are to be drawn concerning chemical 

 changes during growth within the cells. 



What, now, is the picture concerning the proportion of the intracellular and 

 extracellular phases of fluid content during the process of senescence as compared 

 with that during the process of growth? Does a comparison bear out the idea that 

 senescence may be the antithesis of growth? 



Lowry et at. (1942) have studied the chemical make-tip of skeletal and cardiac 

 muscle in senile rats (988 days) compared with those of middle age (603 days). 

 They fotind an increase in water, sodium, and chloride and a decrease in acid- 

 soluble phosphorus and potassium. On a histochemical interpretation, this means 

 that the extracellular fluid has almost doubled, while no essential change has taken 

 place in the water-content of the fibers. There has been a moderate increase in 

 concentration of lipid in the tissue, a change which, like that of the extracellular 

 fluid, is the reverse of the change seen with growth. 



The increase in extracellular fluid with aging may be considered as due prob- 

 ably to histological changes occurring during growth. In other words, loss of 

 individual fibers and atrophy of fibers may account for this increase. 



An experimental study by Hines and Knowlton (1937) on the effects of atrophy 



