756 
DR. CARPENTER ON THE MUTUAL RELATIONS OF 
table structures has produced, are destined for a much higher purpose than that of 
being merely given back to the inorganic universe by eremacausis or combustion. In 
serving as the food of Animals, they not merely become the materials of their struc- 
tures, but are rendered subservient to the production of the nervous and muscular 
forces. The animal, like the plant, receives heat from external sources ; and this is 
expended, in the form of vital force, not merely in the building-up of the organism 
from its germ, but also in its subsequent maintenance. For, as was first definitely 
stated by Prof. Liebig, the vital force, which is applied in Plants to the extension of 
the structure, is appropriated in Animals to the development of muscular and nervous 
power ; and this development, depending as it does upon a continual disintegration 
of the tissues which are its instruments, requires as continual a reconstruction of 
them, Tlie organizing force required for this reconstruction or maintenance, appears, 
like that employed in the original operations of development, to be supplied by Heat; 
and it is a confirmation of this view, that we should find a provision (in those classes 
of animals which are constructed for the greatest development of nervo-muscular 
power) for the maintenance of a constantly high temperature, by the combustion of 
a portion of the organic compounds supplied to them as food. — Of the amount of light 
which is appropriated by Animals, we have no means of forming an estimate ; but 
from the limited nature of its action on their economy, it probably bears an insignifi- 
cant proportion to that which is applied to the purposes of vegetable nutrition. Thus, 
then, the forces on which the animal is essentially dependent, are the affinities which 
hold together the elements of its food, and which are embodiments (so to speak) of 
the light and heat by whose agency they were combined ; the heat, which it derives 
in part from the physical universe, and in part from the combustion of some of its 
alimentary materials ; and the small amount of light required by them, which is sup- 
plied from external sources alone. These forces may be considered as in a state of 
continual restoration during the whole life of animals, in the heat, light, and electri- 
city, and still more in the motion, which they develope ; and, after their death, in the 
production of heat and light during the processes of decay. During animal life there 
is a continual restoration to the inorganic world of carbonic acid, water, and ammo- 
nia ; and the amount thus given up by the animal organism bears an exact propor- 
tion, on the one hand, to the amount of heat and motion which are generated by it, 
and on the other to the amount of organic compounds consumed as food. So that, 
on the whole there is strong reason to believe that the entire amount of force of all 
hinds (as of materials) received by an animal during a given period, is given bach by it 
during that period, his condition at the end of the term being the same as at the be- 
ginning. And all that has been expended in the building up of the organism, is given 
back by its decay after death. 
In bringing this communication to a close, the author would remark, that he has 
not sought in it to increase the knowledge of existing facts, so much as to develope new 
