INADEQUACY OP NATURAL SELECTION, ETC. 639 



ances for solution, depuration, absorption, and circulation, to 

 yield to the multiplying- somatic cells a rich and pure blood. 

 Then we come to an all-important factor, the cost of obtaining 

 food. Here large expenditure of energy in locomotion is necessi- 

 tated, and there but little here great efforts for small portions 

 of food, and there small efforts for great portions : again result- 

 ing in physiological poverty or physiological wealth. Next, 

 beyond the cost of nervo-muscular activities in foraging, there is 

 the cost of maintaining bodily heat. So much heat implies so 

 much consumed nutriment, and the loss by radiation or conduc- 

 tion, which has perpetually to be made good, varies according to 

 many circumstances climate, medium (as air or water), covering, 

 size of body (small cooling relatively faster than large) ; and in 

 proportion to the cost of maintaining heat is the abstraction from 

 the supplies for cell-formation. Finally, there are three all- 

 important co-operative factors, or rather laws of factors, the 

 effects of which vary with the size of the animal. The first is 

 that, while the mass of the body varies as the cubes of its dimen- 

 sions (proportions being supposed constant), the absorbing surface 

 varies as the squares of its dimensions ; whence it results that, 

 other things equal, increase of size implies relative decrease of 

 nutrition, and therefore increased obstacles to cell-multiplication.* 

 The second is a further sequence from these laws namely, that 

 while the weight of the body increases as the cubes of the dimen- 

 sions, the sectional areas of its muscles and bones increase as 

 their squares ; whence follows a decreasing power of resisting 

 strains, and a relative weakness of structure. This is implied in 

 the ability of a small animal to leap many times its own length, 

 while a great animal, like the elephant, cannot leap at all : its 

 bones and muscles being unable to bear the stress which would 

 be required to propel its body through the air. What increasing 

 cost of keeping together the bodily fabric is thus entailed, 

 we cannot say ; but that there is an increasing cost, which 

 diminishes the available materials for increase of size, is beyond 

 question, f And then, in the third place, we have augmented 

 expense of distribution of nutriment. The greater the size 

 becomes, the more force must be exerted to send blood to the 

 periphery ; and this once more entails deduction from the cell- 

 forming matters. 



* Principles of Biology, 46, (No. 8. April, 1863). 



f Ibid. This must not be understood as implying that while the mass 

 increases as the cubes, the quantity of motion which can be generated increases 

 only as the squares ; for this would not be true. The quantity of motion is 

 obviously measured, not by the sectional areas of the muscles alone, but by 

 these multiplied into their lengths, and therefore increases as the cubes. But 

 this admission leaves untouched the conclusion that the ability to bear stress 

 increases only as the squares ; and thus limits the ability to generate motion, 

 by relative incoherence of materials. 



