296 CLASSICS OF MODERN SCIENCE 

 fat, are really only materials for warming, and are perhaps not to 

 be superseded by coal, simply because the latter does not permit itself 

 to be dissolved. 



If, then, the processes in the animal body are not in this respect to 

 be distinguished from inorganic processes, the question arises, whence 

 comes the nutriment which constitutes the source of the body's force? 

 The answer is, from the vegetable kingdom ; for only the material of 

 plants, or the flesh of plant-eating animals, can be made use of for 

 food. The animals which live on plants occupy a mean position be- 

 tween carnivorous animals, in which we reckon man, and vegetables, 

 which the former could not make use of immediately as nutriment. 

 In hay and grass the same nutritive substances are present as in meal 

 and flour, but in less quantity. As, however, the digestive organs 

 of man are not in a condition 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 useful form. 

 In answer to our question, therefore, we are referred to the vegetable 

 world. Now when what plants take in and what they give out are 

 made the subjects of investigation, we find that the principal part of 

 the former consists in the products of combustion which are gen- 

 erated by the animal. They take the consumed carbon given off in 

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

 as water, the nitrogen in its simplest and closest combinations as 

 ammonia; and from these materials, with the assistance of small in- 

 gredients which they take from the soil, they generate anew the com- 

 pound 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 mechanical forces. 

 Would not the combination of both organic kingdoms produce the 

 perpetual motion? We must not conclude hastily: further inquiry 

 shows, that plants are capable of producing 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, — 



