THE VITAL AND PHYSICAL FORCES. 
755 
a part, but all the forces, which are operative in producing the phenomena of life, 
are in the first place derived from the inorganic universe, and are finally restored to 
it again. The author thinks it not difficult to show that such is actually the case ; 
the very same antagonism existing, in respect to the relation of the Vegetable and 
Animal kingdoms respectively, to the forces of the universe, as exists in regard to 
their material components. Plants, it will be recollected, form those organic com- 
pounds at the expense of which animal life (as well as their own) is sustained, by the 
decomposition of carbonic acid, water, and ammonia ; and the light, by whose agency 
alone these compounds can be generated, may be considered as metamorphosed into the 
chemico-vital affinity by which their components are held together. The heat which 
plants receive, acting through their organized structures as vital force, serves to aug- 
ment these structures to an almost unlimited extent, and thus to supply new instru- 
ments for the agency of light and for the production of organic compounds. The 
whole nisus of vegetable life may be considered as manifested in this production ; and 
in effecting it, each organism is not only drawing material, but force, from the uni- 
verse around it. Supposing that no animals existed to consume these organic com- 
pounds, they would be all restored to the inorganic condition by spontaneous decay, 
which would reproduce carbonic acid, water, and ammonia, from which they were 
generated. In this decay, however slow, the same amount of Heat would be given 
off, as in more rapid processes of combustion ; and the faint luminosity which has 
been perceived in some vegetable substances in a state of eremacausis, makes it pro- 
bable that the same is true of Light. And though the process of decay may be pre- 
vented or modified, so that the whole or a part of the materials of vegetable structures 
are disposed of in other ways, yet whenever they return to the condition from which 
they were at first withdrawn, they not only give back to the inorganic world the ma- 
terials out of which they were formed, but the light and heat to which their produc- 
tion was due. Thus in making use of the stores of Coal which have been prepared 
for his wants by the luxuriant flora of past ages, man is not only restoring to the at- 
mosphere the carbonic acid, the water, and the ammonia which it must have con- 
tained in the carboniferous period, but is artificially reproducing the Light and Heat 
which were then expended in the operations of vegetable growth. That the relative 
proportion of the light and heat thus restored, should be the same as that which they 
originally bore to each other, is by no means necessary ; since each (according to 
Prof. Grove’s views) is convertible into the other*'. In the few cases in which motion 
is affected by the vital force of plants, this may be considered as restoring to the in- 
organic universe a certain measure of the force which they have derived from it, in 
the form of light and heat. 
But the organic compounds which the agency of Light and Heat upon the Vege- 
* [In the second edition of his Essay on the “ Correlation of the Physical Forces,” just published, Prof. Grove 
advances the opinion (p. 59) that when Light is “ absorbed ” (to use the ordinary phraseology), that is, when it 
ceases to manifest itself as light, it is usually converted into Heat. — Nov. 20, 1850.] 
5 D 2 
