g60 GROWTH AND THE AGING PROCESS I4 



TABLE 3 



DISTRIBUTION OF CELLS, WATER, AND POTASSIUM IN THE LEFT CARDIAC 

 VENTRICLE OF YOUNG AND ADULT DOGS 



All figures corrected for blood and fat 



* Average age = 187 days. 



Prior to the work of lob and Swanson, other workers had studied the chloride 

 content and dry weight, but this had not always been done for the same fetuses. Aron 

 (1927), however, summarized these results, and they agree in general with the 

 later study of lob and Swanson. They indicate that at a fetal weight of 250 g, the 

 quantity of cells per kilogram of "net" tissue (with corrections for fat, bone, and 

 extracellular solids) is only about 325 g, while at term this proportion has risen 

 to 480-580 g. It continues to rise after birth to reach the adult level of approximately 

 700 g of cells per kilogram of the "net" tissue. These figures support the concept 

 that cells vary in their abundance or concentration during growth without much 

 change in the water content of the individual cells. 



Not only for the body as a whole have such data been obtained, but also for 

 several individual tissues. Hines and Knowlton (1939) studied the water content 

 of skeletal muscle of the rat, using animals ranging from 15-336 days of age. They 

 found very constant figures for the water present within individual fibers but a 

 decreasing proportion of water outside of the fibers (extracelhdar fluid). Yannet 

 and Darrow (1938) found a similar change in the skeletal muscle of the cat (Table 

 2). Their histological observations showed an increase in size of the individual 

 muscle fibers and a relative decrease in size of the spaces between the fibers. 

 Apparently the new cytoplasm added to the fibers is of composition similar to 

 that already present. Similar but much less marked decrease in extracellular 

 fluid seems to occur in liver and brain of the cat, without change in the fluid 

 content "per cell". 



A study on cardiac muscle tissue of the dog (Hastings, Blumgart, Lowry and 

 Gilligan, 1939) showed that here, too, there is a decrease in amount of water in 

 the tissue and that the water content of the muscle fibers themselves remains 

 essentially constant. The proportion of fibers apparently rose from 739 g/kg in the 

 case of puppies to 798 g/kg in the case of adult dogs (Table 3). 



