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XXI.—Observations on the Principle of Vital Affinity, as illustrated by recent 
discoveries in Organic Chemistry. By Witit1amM PuLrenry Atison, M.D., 
F.R.S.E., Professor of the Practice of Medicine mm the Unwersity of Edin- 
burgh. 
(Read 1st and 15th February 1847.) 
Part II. 
It may be remembered that, in the paper formerly laid before this Society on 
this subject, I endeavoured to establish the principle still disputed by some phy- 
siologists, that the laws which regulate the chemical relations, as well as those 
which regulate the visible movements of the particles of matter, undergo a cer- 
tain determinate modification or change in living bodies, which is essential to the 
commencement and to the maintenance of the organization of those bodies; and 
farther, that I undertook the task of attempting to deduce, from the numerous 
but somewhat discordant experiments and observations lately made on the sub- 
ject, certain inferences which appear to be well ascertained, although not gene- 
rally admitted, as to the essential nature of this change, 7. ¢., as to laws which 
regulate those chemical actions which are peculiar to the state of life, and essen- 
tial to the maintenance of organization, both in vegetables and animals. 
In confirmation of my statement of the general principle of Vital Affinity, as 
distinguished from simply chemical affinities, I have much satisfaction in quot- 
ing two sentences from the last edition of LrzBie’s “ Animal Chemistry.” Some of 
the statements of general principles made by this author, seem to me open to ob- 
jection, and some I do not profess to understand; but the following is simple 
and precise ; and, considering the authority of LirBic as a chemist, may, I think, 
be held nearly decisive as to the soundness of the principle. “A fundamental 
error, committed by some physiologists is, that they suppose the chemical and 
physical forces alone, or in combination with anatomy, sufficient to explain the 
phenomena of vitality. It is, indeed, difficult to understand how the chemist, 
who is intimately acquainted with chemical forces, should recognise in the living 
body the existence of new laws, of new causes, while the physiologist, who is 
little or not at all familiar with the action and nature of chemical and physical 
forces, should think himself ready to explain the same processes with the aid of 
the laws of inorganic nature alone.”—Animal Chemistry (third edition, p. 252.) 
The first and most fundamental of these general principles (iikewise consi- 
“dered in my former paper) is the power of vegetable life, under the influence of 
light, to decompose the carbonic acid existing in the atmosphere,—set the oxygen 
free, fix the carbon, and form with it and the elements of water, starch, sugar, 
gum, and the analogous compounds. Our knowledge of this power, of the effects 
VOL. XVI. PART III. 4H 


