LECTURE XXXIV. 



CHEMISTRY. 



VEGETABLE AND ANIMAL SUBSTANCES. 



THE simple substances which enter into the 

 composition of vegetable bodies are very few. As 

 constituent matters, we may confine them to car- 

 bon, hydrogen, oxygen, and nitrogen ; and the 

 latter exists in very small quantities. In animal 

 bodies the list may be increased, as phosphorus 

 and lime enter in considerable quantities, at least 

 into the composition of the solid parts, as the 

 bones, &c. The alkalies also, and some of the 

 metals, are found in animal and vegetable bo- 

 dies, but the latter in too small proportions, and 

 too casually dispersed, to allow us to regard them 

 as constituent parts. 



From these few simple principles, however, a 

 diversity of compounds are formed. It will con- 

 duce much to perspicuity to treat separately of 

 vegetable and animal substances. The phy- 

 siology of both is foreign to the object of these 

 lectures. Chemistry is concerned with them 

 only when they have ceased to live. It treats 

 of the substances of which they are composed, 

 and of the changes which these substances un- 

 dergo. 



