80 ASSIMILATION IN CAKNIVORA. 



the greater part of the earth of bones is obtained by 

 the direct assimilation of phosphate of lime, while 

 the soluble phosphates are better adapted for the 

 production of nervous matter. 



In the graminivora, therefore, whose food con- 

 tains so small a proportion of phosphorus or of 

 phosphates, the organism collects all the soluble 

 phosphates produced by the metamorphosis of tis- 

 sues, and employs them for the developement of the 

 bones and of the phosphorised constituents of the 

 brain ; the organs of excretion do not separate these 

 salts from the blood. The phosphoric acid which, 

 by the change of matter, is separated in the uncom- 

 bined state, is not expelled from the body as phos- 

 phate of soda ; but we find it in the solid excre- 

 ments in the form of insoluble earthy phosphates. 



XVI. If we now compare the capacity for in- 

 crease of mass, the assimilative power in the grami- 

 nivora and carnivora, the commonest observations 

 indicate a very marked difference. 



A spider, which sucks with extreme voracity the 

 blood of the first fly, is not disturbed or excited by 

 a second or third. A cat will eat the first, and per- 

 haps the second mouse presented to her, but even 

 if she kills a third, she does not devour it. Exactly 

 similar observations have been made in regard to 

 lions and tigers, which only devour their prey when 

 urged by hunger. Carnivorous animals, indeed, re- 

 quire less food for their mere support, because their 



