68 [Sknate 



tion of plants. Of these the first is Carbon. This forms from 40 to 

 50 per cent by weight, of the plants cultivated for food; and is there- 

 fore most important to animals and to man. The second of these sim- 

 ple substances, is Oxygen. The quantities of this substance are im- 

 mense; and though we are acquainted with it only in the form in 

 which it exists in the air, nearly one-half of the solid crust of the globe, 

 21 per cent of the atmosphere, eight pounds in every nine of water, 

 and more than one-half of the living bodies of all plants and animals, 

 are oxygen. Hydrogen is the third substance peculiar to plants. 

 This is the lightest of known substances, and forms a small part of the 

 weight of all animal and vegetable bodies; constitutes one-ninth part 

 of the weight of water, but enters mtothe composition of none of the 

 masses that go to form the crust of the globe, coal excepted. The 

 fourth simple substance, entering into the formation of plants, is JVi- 

 trogen. This forms 79 per cent of the bulk of the atmosphere, con- 

 stitutes part of most animal and some vegetable substances; is found 

 in coal to the amount of one or two per cent, but does not exist in 

 any other of the mineral masses constituting the crust of the globe. 

 Although not an abundant substance, the importance of it is not the 

 less decided, and some of its functions are of the most indispensable 

 kind. Plants then, are composed of carbon, oxygen, hydrogen, and 

 nitrogen; the first derived from carbonic acid, the second from the 

 atmosphere, the third from the decomposition of water, and the fourth 

 from ammonia absorbed by water, and taken up by the roots of the 

 vegetables. Some of the earths are occasionally detected in plants, 

 and salts of some kind are always present. In the preparation of ma- 

 nures, the principal object to be aimed at, it is evident, must be to 

 supply the materials needed to furnish the carbon and the ammonia; 

 and these are found in the greatest abundance in dead or decomposed 

 animal and vegetable matter. 



It seems to be a law of nature, that the higher the grade of the 

 animal, or the more complicated its organization, the greater the 

 L wofNu- necessity of a corresponding degree of organization in the 



trition. substances used as food: indeed the manner in which the 

 crude materials, found in the earth and atmosphere, are worked up 

 by plants into a state suitable for conversion into the flesh of animals 

 or food for man, exhibits the strongest proofs of benevolent design 

 in the formation of such grades of organized matter. Man can, in- 

 deed, live on plants, but his teeth demonstrate that flesh was to con- 



