H. Hehnholtz on the Interaction of Natui^al Forces. 209 



not differ from tlie steam-engine, as regards the manner in which 

 it obtains heat and force, but does differ from it in the manner 

 in which the force gained is to be made use of The body is^ 

 besides, more limited than the machine in the choice of its fuel ; 

 the latter could be heated with sugar, with starch-flour, and 

 butter, just as well as with coal or wood ; the animal body must 

 dissolve its materials artificially, and distribute them through its 

 system ; it must, further, perpetually renew the used-up mate- 

 rials of its organs, and as it cannot itself create the matter neces- 

 sary for thisy the matter must come from without. Liebig was 

 the first to point out these various uses of the consumed nutri- 

 ment As material for the perpetual renewal of the body, it 

 seems that certain definite albuminous substances which appear 

 in plants, and form the chief mass of the animal body, can alone 

 be used. Thej form only a portion of the mass of nutriment 

 taken daily; the remainder, sugar, starch, 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 materials for warming, and are perhaps not to be superseded by 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 dis- 

 solved. 



If, then, the processes in the animal body are not in this re- 

 spect 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 king- 



dom; 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 positioa between 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 

 fire 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, per- 

 mit 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 w^orld. Kow 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 com- 

 bustion which are generated by the animal. They take the con- 

 sumed carbon given off in respiration, as carbonic acid, from the 

 air, the consumed hydrogen as water, the nitrogen in its simplest 

 and closest combination xis ammonia; and from these materials, 

 ■^vith the assistance of small ingredients which they take from 





the soil, they generate anew the compound combustible substan- 

 <^es, albumen su^-ar, oil, on which the animal subsists. Ilere, 

 therefore, is a cir° uit which appears to be a perpetual store of 



SECOJHD SERIES, VOL. XXIV, NO. 71. — SEPT., 1857. 



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