Dr Dayy'3 Agricultural Discourse. 291 



ducers of organic compounds for tjae support of animal life. 

 Taking another view, animals may be considered as perform- 

 ing a part as essential to vegetable life, that of disorgan- 

 izers ; what is excrementious from them being so reduced 

 as to have the character rather of inorganic than of organic 

 compounds, whether it be carbonic acid with which they con- 

 taminate the air in respiration, their gaseous excrement, or 

 their liquid and consistent, derived from the other excreting 

 organs and passages of the body. These matters which arc 

 destructive to animals, and not only to the animals that void 

 them, but to animals generally, may be held to be the highest 

 kind and most appropi*iate food of plants. And the more we 

 reflect on this, the more we are convinced of its truth — the 

 more we must admire the connection and mutual depend- 

 ence. The animal enriching the air for the use of the plant, 

 the plant purifying the air for the use of the animal, and 

 the same in regard to the soil, afford a lesson to man of a 

 very instructive kind, most beneficial when carried practi- 

 cally into effect, most injurious when neglected ; in the one 

 instance insuring fertility, and I may add salubrity ; in the 

 other, the production of sterility and disease. 



Let us now, for a moment, take a glance at the composi- 

 tion of plants and animals. Both may be considered as c^im- 

 posed of nearly the same elements, — few in number, but va- 

 riously united, so as to give rise to very many different com- 

 pounds. The principal constituent elements of both are car- 

 bon, hydrogen, and azote, oxygen, lime, potash, silica, and 

 phosphorus. Of these, carbon and silica preponderate in 

 plants (silica, indeed, strictly is confined to plants) ; azote 

 and phosphorus preponderate in animals. In plants, a large 

 proportion of carbon and silica are expended in forming the 

 woody fibre, the framework of the vegetable structure, and 

 the epidermis, the resisting outer covering ; whilst in ani- 

 mals, the azote and phosphorus are .as largely expended in 

 producing the organs of locomotion, — the muscles and bones. 

 And in each instance we witness the usual happy economy 

 of nature, and fitness of means to an end. Plants being 

 fixed to the soil, take from it that which is almost always 

 abundant in a fertile soil, silica y a substance, even in a thin 



