14 PHYSIOLOGY. 



a horse, a cow, a tree, or a rose. They differ so much from 

 all other kinds, that we are seldom in danger of mistaking 

 them. This will not apply to inorganic bodies, except, 

 perhaps, to a few minerals which crystallize in a certain 

 shape. 



5. In organized bodies, we find the parts of which they 

 are composed, distinguished by round or oval forms ; as the 

 body and leaves of trees ; the petals of flowers ; the bodies 

 and limbs of animals. We scarcely ever see straight lines, 

 or sharp angles among them, as in mineral substances. 



Every species of animal or vegetable has its own proper 

 size, from which it varies but little. But minerals may be 

 large or small ; the substance called granite, for example, 

 may make a pebble or a mountain. 



6. Inorganic bodies contain either a single element, as 

 carbon, sulphur, &c., or several of the elementary or simple 

 substances, which are fifty -two in number, as lime, silex, and 

 magnesia ; while in organized bodies, we find at least three 

 of these elements, as carbon, hydrogen, and oxygen in veget- 

 ables ; and the same, with the addition of azote or nitrogen 

 in animals. In organic bodies, there have been discovered 

 in all eighteen simple substances, though they generally con- 

 tain but three or four. 



7. But these two classes of substances, not only differ as 

 to the number of the elements which enter into their com- 

 position, they also differ, as to the mode in which these 

 elements are combined. Thus in minerals, two element- 

 ary substances unite and form a compound, and this again, 

 combines either with another simple substance, or with a 

 compound composed of two other simple substances. Thus, 

 for example, carbonate of ammonia is composed of car- 

 bon, oxygen, hydrogen, and nitrogen, but combined as 

 follows : 



The carbon and oxygen unite to form carbonic acid ; the 

 hydrogen and nitrogen, to form ammonia ; these two com- 

 pounds thus uniting, form carbonate of ammonia. 



