CHAPTER VIII. 



ANTAGONISM BETWEEN EXPENDITURE AND GENESIS. 



§ 347. Under this head we have to set down no evidence 

 derived from the vegetal kingdom. Plants are not expenders 

 of force in such degrees as to affect the general relations with 

 which we are dealing. They have not to maintain a heat 

 above that of their environment, nor have they to generate 

 motion; and hence consumption for these two purposes does 

 not diminish the stock of material which serves on the one 

 hand for growth and on the other hand for propagation. 



It will be well, too, if we pass over the lower animals: 

 especially those aquatic ones which, being nearly of the 

 same temperature as the water, and nearly of the same 

 specific gravity, lose but little in evolving motion, sensible 

 and insensible. A further reason for excluding from con- 

 sideration these inferior types, is that we do not know enough 

 of their rates of genesis to permit of our making, with any 

 satisfaction, those involved comparisons here to be entered 

 upon. 



The facts on which we must mainly depend are those to be 

 gathered from terrestrial animals, and chiefly from those 

 higher classes of them which are at the same time great 

 expenders and have rates of multiplication about which our 

 knowledge is tolerably definite. We will restrict ourselves, 

 then, to the evidence which Birds and Mammals supply. 



§ 348. Satisfactory proof that loss of substance in the 



467 



