﻿206 Proceedings of the Royal Physical Society. 



plication to the Growth of a Multicellular Organism, — It is 

 convenient here to draw attention to the importance of 

 these laws of cell growth and of multiplication with 

 regard to the growth processes of a multicellular organism. 



From what has been said with regard to the growth of 

 the cell, it follows that true hypertrophy, that is, increase 

 in bulk of an organ or organism dependent upon an increase 

 in the size of the component cells, their number remaining 

 constant, depends upon an increase in the supply of food, 

 or upon a supply of more absorbable food, or, that as a 

 result of food already absorbed, the cell becomes more 

 absorptive, in short, that as the result of a more favourable 

 environment, the cell metabolism becomes relatively anabolic. 

 Katabolic growth, that is, increase in cell numbers with 

 reduction of cell size or relative increase of cell surface, 

 has the exactly opposite environmental significance, and 

 corresponds to a relatively less abundant supply of food, 

 or a supply of less absorbable food, or to a diminished 

 absorptive power. 



All the somatic cells of a multicellular organism, however, 

 belong to a race which, under ordinary physiological con- 

 ditions, is doomed to become senile and ultimately extinct. 

 This can be expressed in terms of metabolism as follows : — 

 In a race of somatic cells there is, generation by generation, 

 a reduction in the amount of the physiological energy of 

 the individual cells, and consequently, although favourable 

 nutrition may delay, it cannot prevent the ultimate death 

 of the cells, in other words, the ultimate triumph of 

 katabolism. This is the essential difference between a race 

 of cells and a race of sexually produced multicellular 

 organisms. 



The application of the first law, a healthy population 

 tends to increase beyond the limits of its food supply, is 

 obviously affected by this law of ultimate katabolic triumph, 

 because its intimate meaning is that a food supply, just 

 equal to the demands of a colony of young, actively absorb- 

 ing cells, will be inadequate for the same colony in old 

 age, unless the cells have decreased in size, or assumed a 



