THE PRINCIPLE OF VITAL AFFINITY. 167 
in despite of—the laws which regulate the changes of dead matter. It is thus that 
we are led to ascribe the visible movements of living bodies to vital powers; not 
because we do not perceive how gravitation, elasticity, or any other known 
causes of movement in dead matter should produce them, but because we do 
perceive, that, in the circumstances in which we see these motions, all those 
principles, deduced from the observation of dead matter, would determine either 
rest, or motion in a different direction from that which really takes place. 
I formerly laid before this Society the grounds of an opinion, then much 
disputed, but now, I think, pretty generally admitted, that there are Attractions 
and Repulsions, as well as contractions, peculiar to the living state: chiefly, but 
not exclusively, observed at those parts where chemical changes are effected in 
living bodies, and connected with these changes; and, without reference to this 
general fact, I maintain that it is impossible to have a right understanding of 
many phenomena of essential importance in physiology and pathology.* 
But the general principle is obviously equally applicable to chemical changes 
as to mechanical movements. It is not, indeed, so easy to ascertain, in regard to 
chemical changes in living bodies, that they are truly inconsistent with the chemis- 
try of dead matter; the science must be allowed to make some progress before 
this can be confidently asserted in regard to any individual chemical change; but 
no one can doubt that, as science advances, it must become possible to say with 
certainty, whether the chemical changes in living bodies are consistent with those 
laws which regulate chemical changes elsewhere, or not; 7. ¢., whether the same 
chemical elements can be so brought together by the chemist, as to tend to the 
same combinations as are found in living bodies; or whether, in his hands, they 
will enter uniformly into other combinations, and form different compounds. 
Farther, it appears to me that, even before any of the recent discoveries, it 
might be legitimately inferred from facts already known, that this last descrip- 
tion is truly applicable, in some cases, to the chemistry of living bodies. It was 
known, for example, that when water, impregnated with carbonic acid and with a 
small proportion of ammonia, is brought into contact with vegetable substances, in 
a certain stage of their existence, the elements of these bodies rapidly combine so 
as to form starch, albumen, and oil, which are added to the substance of the vege- 
tables,—that under no other circumstances can water, carbonic acid, and ammo- 
nia, or their elements, be made to form these compouds,—and farther, that after 
a time, when brought into contact, at the same temperature, with the same vege- 
table substance in an ulterior stage of its existence, they will form no such com- 
* Professor WHEWELL, in his instructive abstract of the general principles ascertained in Physio- 
logy, regards it as established, chiefly on the authority of MiiLiER, in regard to the vital force concerned 
in assimilation and secretion, that “« it has mechanical efficacy, producing motions, &c. But it exerts 
at the same point both an attraction and a repulsion, attracting matter on one side and repelling it on 
the other ; and in this it differs entirely from mechanical forces."—Philosophy of Inductive Sciences, 
vol. i1., p. 51. See also Carrenter’s Manual of Physiology, § 597, et seq. 
