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vegetables, which the former could not make use of immedi 

 ately as nutriment. In hay and grass the same nutritive sub 

 stances are present as in meal and flour, but in less quantity. 

 As, however, the digestive organs of man are not in a condi 

 tion to extract the small quantity of the useful from the great 

 excess of the insoluble, we submit, in the first place, these 

 substances to the powerful digestion of the ox, permit the 

 nourishment to store itself in the animal s body, in order in 

 the end to gain it for ourselves in a more agreeable and use 

 ful form. In answer to our question, therefore, we are re 

 ferred to the vegetable world. Now when what plants take 

 in and what they give out are made the subjects of investiga 

 tion, we find that the principal part of the former consists in 

 the products of combustion which are generated by the ani 

 mal. They take the consumed carbon given off in respira 

 tion, as carbonic acid, from the air, the consumed hydrogen 

 as water, the nitrogen in its simplest and closest combination 

 as ammonia ; and from these materials, with the assistance 

 of small ingredients which they take from the soil, they gen 

 erate anew the compound combustible substances, albumen, 

 sugar, oil, on which the animal subsists. Here, therefore, is 

 a circuit which appears to be a perpetual store of force. 

 Plants prepare fuel and nutriment, animals consume these, 

 burn them slowly in their lungs, and from the products of 

 combustion the plants again derive their nutriment. The 

 latter is an eternal source of chemical, the former of mechan 

 ical forces. Would not the combination of both organic king 

 doms produce the perpetual motion ? We must not conclude 

 hastily : further inquiry shows, that plants are capable of pro 

 ducing combustible substances only when they are under the 

 influence of the sun. A portion of the sun s rays exhibits a 

 remarkable relation to chemical forces, it can produce and 

 destroy chemical combinations ; and these rays, which for the 

 most part are blue or violet, are called therefore chemical 

 rays. We make use of their action in the production of pho* 



