death and subsequent decomposition of their bodies, and by 

 the constant removal, in various ways, of effete ejecta, 

 matter which has previously existed in the state of organic 

 compounds in animal bodies, is constantly being reduced 

 to an inorganic state. Were it not the case, therefore, 

 that the vegetable kingdom continually produces fresh sup- 

 plies of organic compounds, animal life must gradually 

 diminish and disappear. Directly, or indirectly, all animals 

 derive their support from vegetable substances. Herbivo- 

 rous animals convert their vegetable food into the materials 

 of their own bodies; and these, in their turn, become the 

 food of the rapacious carnivora. 



The conversion of the flesh of one animal into the living 

 body of another, by the digestive and assimilative processes, 

 may seem to be a change simple and easily effected, the 

 organic chemical principles of which both are composed 

 being the same. But the conversion of vegetable substances 

 in the bodies of herbivora, into their own tissues, has been 

 generally supposed to require a greater change in the chem- 

 ical composition of such aliments, and to imply a greater 

 exercise of vital chemistry. Modern researches, however, in 

 organic chemistry, (and more particularly by Liebig, who has 

 added so much to our knowledge in this branch of the science,) 

 have shown that those chemical principles, of which the tissues 

 of animals are built up, are present in vegetable substances, 

 though, in such, forming only a small proportion of the 

 whole ; but most abundant in those which are best adapted 

 to serve as food for animals. 



As this is one very important illustration of our subject, — 

 showing how intimate and exact are the adaptations of one 

 of the great kingdoms of organized beings to the require- 

 ments of the other, — I shall attempt a very brief outline of 

 the facts bearing upon this point. 



The principal chemical compounds containing nitrogen, or 

 azote, of which the tissues of animals consist, are albumen, 



T 2 



