﻿Bones of the Skeleton as an Index of Nutrition. 205 



possesses, or, in other words, upon the start which anabolism 

 gets at the outset, but varies directly as the surplus of 

 nutrition over expenditure, and directly as the rate at 

 which this surplus decreases. The moment the surplus of 

 nutrition over expenditure falls below zero the cell must 

 die or divide. The moment division takes place the problem 

 becomes complicated by the action of the laws governing 

 the multiplication of living organisms. 



(b) The Laws of the Multiplication of Living Organisms. — 

 Before proceeding to discuss farther the problems of growth, 

 it is necessary, briefly, to state the laws of multiplication. 

 The first of these is a modification of the law of Malthus. 

 It reads : " A healthy population tends to increase to the 

 limits of its food supply." The second is : " Since all living 

 organisms have a fixed period to their individual existence, 

 they must, in order to exist at all, establish with their 

 environment an equilibrium sooner or later to be overthrown 

 in death." The corollary of this is, " to prevent extinction 

 the organism must meet the effects of its environment in 

 two ways, by individual adaptation and by genesis." The 

 third law is important: it is, "When favourable circumstances 

 cause any species to become unusually numerous, com- 

 petition becomes keener, and enemies that prey upon it 

 more abundant." The fourth is : "In a species which sur- 

 vives, given the forces destructive of race as a constant 

 quantity, those preservative of race must be a constant 

 quantity also, and since the latter are two, the individual 

 and the reproductive, these must vary inversely." To this 

 law every species must conform or cease to exist. Tersely 

 restated it reads, " Individuation and genesis vary inversely." 

 The corollaries are (first) "Advancing specialisation must 

 be accompanied by declining fertility;" and (second) "If 

 the difficulties of self-preservation permanently diminish, 

 there will be a permanent increase in the rate of multi- 

 plication, and conversely." ^ 



(c) Application of the Laws of Cell Growth and of Multi- 



1 Geddes and Thomson, The Evolution of Sex. 



