GROWTH. 161 



trasted in their amounts; and the two diminishing series of 

 such increments end at similarly-contrasted limits. 



§ 49. Such are the several conditions by which the phe- 

 nomena of growth are determined. Conspiring and conflict- 

 ing in endless unlike ways and degrees, they in every case 

 qualify more or less differently each other's effects. Hence it 

 happens that we are obliged to state each generalization as true 

 on the average, or to make the proviso — other things equal. 



Understood in this qualified form, our conclusions are 

 these. First, that growth being an integration with the 

 organism of such environing matters as are of like natures 

 with the matters composing the organism, its growth is de- 

 pendent on the available supply of them. Second, that the 

 available supply of assimilable matter being the same, and 

 other conditions not dissimilar, the degree of growth varies 

 according to the surplus of nutrition over expenditure — a 

 generalization which is illustrated in some of the broader 

 contrasts between different divisions of organisms. Third, 

 that in the same organism the surplus of nutrition over 

 expenditure differs at different stages; and that growth is 

 unlimited or has a definite limit, according as the surplus 

 does or does not rapidly decrease. This proposition we found 

 exemplified by the almost unceasing growth of organisms 

 that expend relatively little energy; and by the definitely 

 limited growth of organisms that expend much energy. 

 Fourth, that among organisms which are large expenders of 

 force, the size ultimately attained is, other things equal, 

 determined by the initial size : in proof of which conclusion 

 we have abundant facts, as well as the a priori necessity 

 that the sum-totals of analogous diminishing series, must 

 depend upon the amounts of their initial terms. Fifth, that 

 where the likeness of other circumstances permits a com- 

 parison, the possible extent of growth depends on the degree 

 of organization ; an inference testified to by the larger forms 

 among the various divisions and sub-divisions of organisms. 



