PROFESSOR WEISMANN'S THEORIES. 479 



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 securing 

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

 sitated, 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, be- 

 yond 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), cover- 

 ing, 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 ef- 

 fects 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 dimensions 

 (proportions being supposed constant), the absorbing surface va- 

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

 things equal, increase of size implies relative decrease of nutri- 

 tion, 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 abil- 

 ity of a small animal to leap many times its own length, while a 

 great animal, like the elephant, can not 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 keep- 

 ing together the bodily fabric is thus entailed, we can not say ; but 

 that there is an increasing cost, which diminishes the available 

 materials for increase of size, in 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 sectioned 

 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 

 strcM increases only as the squares, and thus limits the ability to generate motion, by rela- 

 tive incoherence of materials. 



