G58 
INTRODUCTORY LECTURE. 
science the physiologist would have ever possessed but little 
actual knowledge of the processes of digestion^ assimilation, 
respiration, &,c.j and it is chemistry alone that informs us of 
the composition of, and of the changes in composition under¬ 
gone in the body by, the different kinds of food, of the saliva, 
gastric juice, bile, blood, urine, and so forth. In confirma¬ 
tion of these statements respecting the influence of chemical 
knowledge on physiological pursuits, I can do no better than 
quote some of the remarks contained in the very admirable 
^Address in Physiology^ delivered last year at the annual 
meeting of the British Medical Association, by the learned 
professor of physiology at University College, London. Dr. 
JSharpey, one of your examiners, gentlemen, and to whom I 
refer, said, in speaking of physiological chemistry, 1 need 
scarcely remark that the spirit of research in that department 
lias been so busy, and the results obtained so vast and so 
varied, that, compared with its importance, my reference to 
the subject must be slight and partial. I may remind you, 
in the first place, of the knowledge gained concerning the 
proximate principles of food; the recognition in plants of 
alburnenoid compounds, in virtue of which vegetable nourish¬ 
ment sustains animal life; the light thrown on the changes 
which nutrient matters undergo in the alimentary canal, fitting 
them for absorption and reception into the blood, and on the 
operation of the salivary, gastric, and pancreatic fluids in 
producing these changes, as well as the discovery of the 
peculiar constituents of those fluids on which their efficacy 
depends.’^ Reference is then made by the learned doctor to 
the broad and luminous views emanating from Liebig and 
his school as to the use, immediate destination, and ultimate 
disposition of the several constituents of the aliment, in 
repairing the consumption of the tissues and maintaining the 
heat of the body; and the final identification, qualitative and 
quantitative, by Schmidt, Boussingault, Barrel, Bischoff, and 
others, of the constituent elements of the nutritive principles 
as discharged by the lungs, kidneys, and skin. It is now 
also shown that these exuvial materials, after being delivered 
over to the earth and atmosphere in the shape of water, 
carbonic acid, and ammoniacal urinary products, become 
available as the food of plants, by which they are again 
combined into proximate principles, and serve anew for the 
sustenance of the animal kingdom; and in this admirable 
cycle of interchange and reciprocal compensation between 
the three kingdoms of nature, we are permitted to see 
another example of that tendency to the maintenance of 
order and stabilit}^ so conspicuous in the phenomena of the 
universe. But, although the chemist thus presents us, as it 
