
THE PRINCIPLE OF VITAL AFFINITY. 331 
excluded from the new combinations which are formed in a living body, or re- 
jected from the selections which are there made. 
Now, if we consider it as ascertained, that a part of all the aliments taken 
into a living animal body, combines immediately with the oxygen of the air, in 
the blood, and is thrown off by the excretions in the form of water, carbonic acid, 
and ammonia,—or in forms which tend towards, and quickly resolve themselves 
into, these compounds,—we see a distinct confirmation of what was formerly 
stated, as to the nature of vital affinity, viz., that it does not, properly speaking, 
supersede ordinary chemical affinities, but is merely superadded to them ; so that 
chemical compounds, taken into animal bodies, are subjected to these attractions 
as well as others, and are divided between the substances thus acting upon them, 
in proportions varying probably, as in other cases, according to the strength of the 
affinities and the quantities of matter exerting them. This, indeed, appears suf- 
ficiently demonstrated by the effect of exercise (already considered) on the excre- 
tions by the skin and lungs, on the one hand, and on the deposition of fat or of 
albuminous compounds, on the other; we know, that, as the quantity of carbonic 
acid and water thrown off are increased by that cause, the quantity of fat de- 
posited from the blood is diminished,—implying that, by the increased quantity 
of oxygen presented to them by the blood, portions of the carbon and hydrogen 
of the ingesta, which would otherwise have been subjected to the vital affinity 
which forms fat, have yielded to the simply chemical affinity which disposes them 
to unite with oxygen and pass off; and again, it is at least highly probable, that, 
under this increased supply of oxygen, increasing, by a simply chemical attrac- 
tion, the proportion of carbon and hydrogen which escape from the ingesta, the 
effect of the vital affinity by which the remaining elements of the ingesta combine 
to form albuminous matter, is likewise increased. 
But we have next to consider the evidence for the existence, and the object 
and importance of another and totally distinct source, long believed to contribute 
to the formation of the excretions, viz., matter which has formed part of the tex- 
tures of the living body, and been re-absorbed from them, with the intention of 
being thrown out of the body; 2. ¢., the dependence of excretion on what Dr Prout 
calls “ destructive assimilation.” 
The mixture, of this matter with the blood appears to be necessary for all 
the changes there, from which the different excreted fluids result; or, it may be 
' supposed not merely to escape itself, but to act as a ferment, promoting these 
changes, and thereby determining the entrance into these combinations, and the 
expulsion from the body, of the portions of the ingesta which are not required 
for nutrition. 
The term efete matter has been very generally employed in discussions on 
this subject ; but it does not appear to me, that any very definite idea has been 
annexed to the term, nor that any principle has been pointed out to explain how 
