OF VITAL FORCE, AND THE CONDITIONS OF ITS EXERCISE. 145 



stores of Coal which have been prepared for his use by the luxuriant Flora of 

 past ages, is reproducing and applying to his own purposes the Light and Heat 

 which sustained the vegetable life of the Carboniferous period, whilst returning 

 to the atmosphere the water, carbonic acid, and ammonia, which were then 

 withdrawn from it. 



126. But the Organic Compounds which the agency of Light and Heat upon 

 the Vegetable fabric has produced, are designed for a much higher purpose than 

 that of being merely given back to the Inorganic universe by decay or combus- 

 tion; and the forces which hold together their elements have a much more ex- 

 alted destiny. In serving as the food of Animals, a part of these compounds 

 become the materials of their organized tissues, and the instruments by which 

 their various forms of Vital power are exercised; and in the greater number of 

 Animals, as in the germinating seed, the Heat which is supplied from without 

 may be looked upon as the ultimate source of the power by which the organ- 

 izing process is carried on. Thus, during the whole period of growth and de- 

 velopment, there is, as in the Plant, a continual augmentation in the amount of 

 Vital action performed ; and the increase of this would be unlimited, were it 

 not checked by a process of a converse character. For the peculiar activity of 

 Animals consists, not in the phenomena of vegetative growth, but, in the per- 

 formance of movements, through the instrumentality of the nervo-muscular 

 apparatus, which is built up by the organizing process; and the execution of 

 these movements involves an expenditure of Vital force, as manifested in the 

 death and disintegration of the nervo-muscular tissues, which appears to be in 

 strict relation to the amount of Physical power thus generated. And thus it 

 happens, that there is, during Animal life, a continual restoration to the Inor- 

 ganic world, of the water, carbonic acid, and ammonia, originally supplied by it 

 as the food of plants ; these being formed by the union of the oxygen of the 

 atmosphere (which was not appropriated by the plant) with the elements of the 

 nervo-muscular tissue, or rather with those of urea, lactic acid, &c., which are 

 the immediate products of their decay ( 91). Not only is Motion thus gene- 

 rated, but also Heat, and (occasionally) Light and Electricity; and thus an 

 Animal which has arrived at its full growth, and which is simply maintaining 

 the standard it has then acquired, is continually restoring to the Inorganic 

 world both the material equivalents of its food, and the dynamical equivalents 

 of the Chemical affinities which held together the elements of this, as well as 

 of the Heat which supplied the organizing force whereby it was converted into 

 living tissue. The final decay of the organism, as in the Plant, will give back 

 both the material and dynamical equivalents of the matter and force which were 

 consumed in its first production, unless its substance should be appropriated as 

 food by another organism ; in which case it serves to the Carnivorous animal 

 precisely the same purposes, as those to which the organic compounds supplied 

 by the Plant are subservient in the Herbivorous animal. 



127. The condition of Man and of all " warm-blooded" animals, however, 

 differs in this important particular from that of " cold-blooded" animals, and of 

 plants. For, whilst the latter are almost entirely dependent for the Heat which 

 is the source of their vital force, upon that which they receive from the solar 

 rays, so that their temperature rises and falls with that of the medium they in- 

 habit, the former are enabled to maintain the heat of their bodies at a constant 

 standard, by combustive processes which take place in their interior, at the ex- 

 pense, not only of the materials of their disintegrated tissues, but also of a por- 

 tion of their food, the non-azotized ingredients of which are chiefly appropriated 

 to this purpose ( 42, 50). And thus we find that whilst the Azotized com- 

 pounds prepared by Plants supply the actual materials for the building-up of 

 the Animal fabric, the Hydro-carbonaceous or non-azotized (starchy, saccharine, 

 oleaginous, &c.), answer the not less important purpose of furnishing, by their 



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