AinBIAL MANURES. i 1 1> 



class of these compoimds, glaten, albumen, &c was distin- \ 

 guished by containing a large amount of nitrogen, and was / 

 in fact almost identical in composition with the substance of \ 

 the flesh of animals, another class of bodies — starch, sugar, [ 

 fat, &c was composed solely of carbon and the elements of \ 

 water united in various proportions. You are already aware r 

 that the gluten, and other nitrogenized matters contained in N 

 the seeds and herbage which are eaten by animals, sei-ve to/ 

 build up their bodies — are converted into their substance;] 

 but in the greater number of plants used for food, the pro- / 

 portion of compounds containing nitrogen is exceedingly small j 

 as compared with those resembling starch and sugar m( 

 composition, the former on an average amounting to only) 

 1 1 per cent, while the latter average from 70 to 80 per cent.S 

 *' What," you will inquire, "becomes of the carbon which is S. 

 eaten by animals?" ) 



173. You may recollect that I stated (26) that an enormous 

 amount of carbonic acid is given out in respiration. The an* _ 

 that we draw into our lungs in breathing contains only the ^. 

 one two-thousand-five-hundredth part of its bulk of that gas ; 

 yet, when we throw it out again into the atmosphere, its 

 proportion is found to be increased so as to form two gallons* 



in every hundred expired ; a full-grown man, using vigorous 

 exercise, giving out every day from his lungs as much 

 carbonic acid as would be produced by the combustion of 

 about fifteen ounces of charcoal. This separation of carbon 

 in the form of carbonic acid from the lungs of animals, is 

 indispensable to the continuance of life, and is made to serve 

 an important purpose in the animal economy. 



1 74. When a pound of starch or sugar is set on fire it 

 bums and disappears, the carbon contained in it unites with 

 the oxygen of the air, producing carbonic acid gas (22) and 

 giving out heat; and the carbonaceous compounds, starch, 

 ttc. which the animal eats, are believed to undergo, within i 

 the hody^ by the intiuence of the oxygen of the inspired air, 

 ]irecisely similar changes as when burned, the carbonic acid 

 i!:a3 being discharged from the mouth and nostrils, while the 

 heat which is generated by their combustion, as it may be 

 t(;rmed, serves to maintain that temperature of the body 

 which health requires. Thus, you perceive that those com- 

 pounds, though incapable of being employed in the formation 

 of bone or muscle, are indispensable to animal life. 



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