52 
IMPORTANCE OF THE STUDY OF CHEMISTRY, 
* * * When glancing, in a former portion of this lecture, at the 
benefits arising to agriculture and medicine from the progress of chemistry, 
I have already hinted at the inquiries which have for their object the exami¬ 
nation of the chemical conditions of vegetal and animal life, aud at the light 
which they have thrown upon the true nature of respiration and nutrition. 
I am inclined to look again at these inquiries from a different point of 
view. They have taught us that animal respiration is a true process of 
combustion; in order to secure the necessary warmth, we have to burn at 
every moment a part of our body ; this source of heat lasts solong as we supply 
to the seat of combustion continually renewed fuel; so long as the alternation 
of breathing maintains the supply of the necessary amount of oxygen, and 
accomplishes the removal of the products of combustion, i. e., of water and 
carbonic acid. With each respiration the animal robs the atmosphere of a 
certain quantity of oxygen, and introduces into it a proportionate bulk of 
carbonic acid. If we consider that the endless processes of combustion, 
carried out for domestic purposes and for the purposes of industry, produce 
the same effect; that, lastly, the transformations of organic matter, which 
we designate as putrefaction and decay, are, in many respects, nothing but 
processes of slow combustion: it is evident that the unlimited continuance 
of these conditions must gradually involve a change in the constitution of 
our atmosphere. Such a change has not yet been observed. It has been 
justly argued that the immense space of the atmosphere necessarily renders 
changes of this sort extremely slow, that our analytical methods are not 
sufficiently accurate, that our experiments do not extend over a sufficient 
length of time; nevertheless, who could fail to perceive that the com¬ 
pensation is furnished by the difference of conditions which govern the life 
of the plant in contradistinction to that of the animal ? With its leaves, 
as with so many lungs, the plant withdraws the carbonic acid from the air. 
Under the influence of sunlight the carbonic acid splits into its constituents 
—the carbon is employed in building up the plant, whilst the oxygen is 
returned into the atmosphere. The plant is referred, for its support, to the 
compound which the animal ejects from its organism as no longer serviceable 
for the purposes of its life; but it requires only a part of this compound; 
the rest is set free, again to take part in the development of a new animal 
generation. 
How simple and how wonderful are the means which Nature employs to 
fulfil her least, as well as her greatest designs 1 
A mine of interesting considerations is opened by the phenomena to 
which we have slightly adverted. The carbon of the plant is derived from 
the air, in which it exists in the form of carbonic acid. The carbonic acid 
is, as we have seen, partly furnished by the respiration of the animal; but 
in combustion as in decay a supply of carbonic acid no less inexhaustible is 
secured to the atmosphere. But with how new a signification do these pro¬ 
cesses become endowed when we view them in relation to vegetal life ! Com¬ 
bustion, which suggests to the ordinary observer the idea of destruction— 
decay, which we are in the habit of considering as the symbol of death, in 
the eye of the chemist are but changes of form bearing the germ of a 
new unfolding of life. Of all the changes which surround us in nature how 
different are the views we take, when once the study of chemical phenomena 
has convinced us of the indestructibility of matter, when once we have 
accustomed ourselves to consider, as fixed and unalterable, the sum of 
matter which, under the influence of the forces of nature in the processes of 
vegetal and animal life, is capable of assuming so endless a variety of form 1 
Contemplations of even a higher order have been attached to this recog¬ 
nition. No one is likely to deny the danger of attempting to refer the con¬ 
ditions of spiritual life to the laws of the material world, still, this speculation, 
which appears so consonant to ordinary conception, has been at all times 
