452 
DR. PROUT ON CHEMISTRY. 
ous action, at least that of the ganglionic nerves; and an in¬ 
finite variety of similar matters, the existence even, much less 
the modus operandi , of which is entirely unknown to us. 
From the little progess that has been made in the philosophy 
of chemistry, and its great difficulty, we must be content, I fear, 
for many years yet to come, with a very limited knowledge of the 
subject. In the meantime, let us inquire very briefly how far 
the art of chemistry, or the consideration of the chemical pro¬ 
perties of bodies, can be best applied to the purposes of physio¬ 
logy and pathology. 
I have already said that the physiologist, in order to obtain 
the utmost advantages that chemistry is capable of contributing, 
must turn chemist himself, and carry on his researches in con¬ 
nexion with the phenomena of life, of which he must never lose 
sight for a moment. In the first place, and whenever it can be 
done, the substance to be examined should be detached from all 
others, and obtained in a crystalline form. On this part of the 
inquiry much valuable practical knowledge is to be obtained by a 
careful study of the essays of preceding celebrated chemists, and 
particularly of the French chemists, who have pursued this 
branch of inquiry farther than it has been carried in this country. 
When a substance cannot be obtained in a crystalline form, which 
is the case with by far the greater proportion of organic matters, 
we are obliged to quit altogether the solid foundation of quantity, 
and to take our station among the uncertainties of mere quality, 
or sensible properties. Now every one must have remarked, at the 
outset of his chemical career, that the phenomena presented even 
by well-defined bodies, when submitted to the action of tests and 
re-agents, were often very different from what he had been led to 
expect; and that, from some trifling circumstance or other, he 
was constantly liable to fall into error; and, in short, in many 
cases, that it was not till after long and close attention that he 
was enabled completely to see his way, and separate the essential 
from the accidental phenomena. Even here, then, much depends 
upon the operator; and according as his skill and experience are 
greater or less, so will his statements be more or less entitled to 
confidence. But if this be the case with fixed and well-defined 
substances, how much more strikingly so is it with organized 
bodies, the phenomena presented by which, whether naturally, 
or as influenced by tests and re-agents, are so delicate and evanes¬ 
cent, so varied and infinite in number, that language is scarcely 
capable of conveying any adequate idea of them : hence the long 
and tedious details of precipitations, changes, &c. said to be pro¬ 
duced by different re-agents on organic products, are, for the 
most part, entirely useless both to the chemist and physiolo- 
