1 1 6 RE GENERA TION 



of the organism itself. Whether the size is due to more cells being 

 present, as seems probable, or to the cells being larger, or to both, 

 has not, so far as I know, been determined for man. In a mollusk, 

 Crepidula fornicata, in which large and small adult individuals occur, 

 it has been shown by Conklin ('98) that the difference is due entirely 

 to the larger number of cells in the larger individual. In this case 

 external conditions, in so far as they retard the maximum possible 

 growth of the individual, are responsible for the differences in size. 

 The distinction is, in this case, rather between large normal indi- 

 viduals and dwarfs, than between giants and normal or average 

 individuals. 



The voluntary muscles of the body of man grow larger, and may 

 be said to hypertrophy, as a result of doing certain kinds of work. 

 The muscles of the hand and arm grow large through use, and 

 become smaller again if not used ; but the muscles of the fingers of a 

 musician do not hypertrophy, although the total amount of work done 

 may be very large. It is only when muscular work is done against 

 great resistance that enlargement of the muscles takes place. The 

 factors that may bring about the enlargement will be discussed later. 



The kidneys seem to give the most satisfactory evidence of com- 

 pensating hypertrophy. Nothnagel 1 states that it has been shown 

 in man, in the rabbit, and in the dog, that when one kidney has been 

 removed the other enlarges; and that this takes place both for young 

 animals, in which the kidneys have not reached their full size, and in 

 adult animals, in which the remaining kidney becomes larger than 

 normal. In the adult the enlargement is due to hypertrophy, in 

 Virchow's sense, in the tubules and in the epithelium of the canals. 

 In the young animal there is, in addition, a hyperplastic growth that 

 leads to an increase in the number of glomeruli, etc. 



Experiments have shown that the same amount of urea is excreted 

 by the animal after the removal of one kidney as before ; in fact, this 

 is true immediately after the operation, before any increase in the 

 size of the organ has taken place. This means that, under normal 

 conditions, the kidneys do not perform their maximum of work. It 

 is important to observe in this connection that the remaining kidney 

 gets more blood than it would get if the other were present. Noth- 

 nagel sums up the changes that take place in this way : First, the 

 removal of one kidney ; second, an increase in the flow of blood in 

 the remaining kidney ; third, an increase in the functional activity and 

 excretion of this kidney ; fourth, along with the increase in the flow 

 of blood, there is a necessary increase in the amount of food that is 



1 Nothnagel gives a review of the subject down to 1886 in an article entitled "Uber 

 Anpassung und Ausgleichting bei palhologischcn Zustanden. Zeilsc/i. f. klinische Medicin" 

 1886. Vols. X and XI. 



