THE PRINCIPLE OF VITAL AFFINITY. 315 
of oxidation, nor a mere selection and appropriation of compounds previously 
formed in vegetables. 
On the other hand, it is known that there is an evolution of carbonic acid as 
well as water from vegetables,—from the parts of fructification during their deve- 
lopment even in the day time, and from all parts during the night ; and it appears 
quite possible that, in both cases, this may be by a process of slow combustion, 
similar to the process of oxidation which Dumas considers as characteristic of 
animal life only. For, although it has been stated by Dumas that the carbonic 
acid given up by vegetables during the night is only what has been absorbed by 
their roots, and passed unchanged through their substance, yet I do not find any 
distinct proof of this in his writings. It is certainly true, that the organic com- 
pounds formed by vegetables, and taken into animal bodies, ultimately undergo 
in them a chemical change nearly equivalent to slow combustion, and are thus 
returned to the inorganic world; but this is in the processes of absorption, de- 
composition, and excretion, of the animal textures, to be considered presently ; and 
this fact affords of itself no proof, that in the previous growth and development 
of animal textures, there may not be an actual formation of albuminous com- 
pounds, as well as of gelatin and fat. 
These facts appear sufficient to shew, that there is no such direct opposition 
between vegetables and animals, as to the chemical results of their vital action, 
as Dumas has represented; and even to make it probable, that, during the or- 
ganic or vegetative life of animals, there will be a formation of albuminous 
matter, equally as of gelatin and fat. 
In fact, this question can be only finally decided by experiments to shew 
whether or not the whole quantity of albumen deposited in the textures of a 
growing animal may be greater than that contained in its food; or whether the 
azote excreted, during a pretty long period, from an animal, by the bowels, kid- 
neys, skin,* and lungst (for it appears to be well ascertained, that, from all these 
parts, there is a frequent, if not an habitual, excretion of azote), is greater, under 
any circumstances, than the quantity of that element contained in the albumi- 
nous portion of its food, which is the only ascertained channel of the introduc- 
tion of azote into the animal system ; and, although this is a difficult inquiry, we 
cannot suppose that the difficulties are insurmountable. If such an excess of ex- 
cretion of azote shall be ascertained, it will be nearly enough to entitle us to con- 
clude that albuminous matters can be formed in the animal body, and yield it 
during their decomposition there. It is not enough to say, that there is no occa- 
sion for more azote in the animal economy than is contained in the albuminous 
ingesta, because what is there contained is already in just the same proportion to 
* See Goxpine Birp on Urinary Deposits, p. 104. 
+ See Du Lone, quoted by Dumas (Organic Nature, p. 106). 
