392 PROFESSOR ALISON’S DEFENCE 
of a more refined and subtle description than any which we can command, and 
may therefore accomplish effects by purely chemical and physical agency, which 
may for ever lie beyond the reach of the coarser manipulations of art; and here 
he refers to HumBoLp?, who says, that, as we do not understand all the conditions 
under which ordinary chemical and physical forces act in living beings, we are 
not entitled to assert that they may not produce all the chemical changes that we 
seein them : to what conditions he here alludes does not appear, but he gives this 
as a reason for renouncing, or, at least, expressing doubts as to the theory of 
vital affinity, which he had formerly espoused, and illustrated by an allegory 
under the name of the Rhodian Genius. 
Dr DauBENy says more precisely, that ‘ the peculiar structure of parts, arising 
out of the Movements induced by a vital principle, may be found competent to 
bring about these phenomena in question, and that it is incumbent on us to in- 
vestigate to the full the extent to which such physical causes can be supposed to 
operate, before pronouncing whether there may not, after all, be some residual 
phenomenon, inexplicable by the common principles of science, and which we must, 
therefore, refer to vital affinity.” But even in regard to movements, from his ex- 
pressions at p. 379, he does not seem to admit that any others are to be ascribed 
to the vital principle, than those which result from Contractility. 
In thus admitting that the movements which take place in living animals, at 
least those which can be referred to contraction of solids, arise out of the vital 
principle (which, I apprehend, means only that they are an ultimate fact,—so 
far as yet known exemplified in no other department of nature); and in as- 
cribing to the peculiarity of those movements the peculiar structure of living 
parts, and through the intervention of that structure the peculiar chemical changes 
of living beings, Dr Dauseny has stated what I believe to be the general idea of 
those physiologists who reject the doctrine of vital affinity. They think that 
having allowed that movements, and particularly contractions of living solids, are 
truly vital phenomena, they have furnished a possible explanation of all chemical 
changes which seem peculiar to life, and that they are entitled to throw on us the 
burden of disproving this theory, before they can be called on to admit any such 
principle as vital affinity modifying chemical laws in the living body. 
To this I reply, jirst, that this theory in explanation of the chemical pheno- 
mena of life is distinctly inadequate. I do not think it can be more distinctly 
stated, or more plausibly supported, than it was by the late Dr Murray, in treat- 
ing of Secretion, who, at the same time, however, distinctly admitted that it was 
*“ hypothesis supported by little direct proof. The cause of production of the new 
combinations which constitute secretion,” he says, “ may be the simple approxima- 
tion of the elements which constitute the blood. That fluid is propelled byt he vis 
a tergo into canals of the most astonishing minuteness, the diameters of which are 
