VEGETATION AND THE ATMOSPHERE. 187 
character it is necessary to add another, which is that receiving as primary 
material carbonic acid and water, substances burnt, plants have the faculty of 
expelling the oxygen and of extracting from them the carbon and hydrogen, 
to which they restore the property of being susceptible of being burnt anew. 
These chemical actions take place within their organs, but these organs are 
only the seat of them; the cause of these actions is without; it proceeds from 
the sun. : 
The animal has received a diametrically opposite mission. It creates not, 
it destroys; in place of solidifying the liquids and gases, it separates them and 
restores them to the atmosphere; in fine, far from bringing back bodies to the 
combustible state, it burns them. The herbivorous animal derives all his nour- 
ishment from plants; he transforms a part of them into water and carbonic 
acid, he accumulates the rest in appropriate organs. ‘The carnivorous profits 
of these reserves, and finishes by restoring to the atmosphere what vegetables 
have extracted from it ; what the herbivores have preserved of it, and whatever 
the class to which it appertains, every animal rejects by the natural ducts an 
abundant provision of azotized matter which it deposits on the soil. It is pre- 
cisely this matter which vegetables take up again, without which they cannot 
live, which they possess the power of elaborating, transforming, accumulating, 
and which they return to animals after having restored to it the nutritive quali- 
ties which it had lost. Thus is closed that admirable circle of opposite trans- 
formations and of mutual services where we see the animal and the vegetable 
eternally exchange the same matter; this, which receives it gaseous, disoxi- 
dizing and solidifying it; that, which receives it combustible, again dispersing 
anew after having burnt it. Priestley saw in plants predestined servitors whose 
office it is to purify the air; but they have another function much more imme- 
diate and render us a service quite otherwise indispensable, that, namely, of 
extracting and prgparing our aliments. Their action on the air would only be 
sensible after a long succession of ages; but if a single year drought annihi- 
lated the fruits of the earth, a frightful famine would destroy in a short time 
all the animals which the globe nourishes. 
From the sun it is that daily nourishment, life, force, and all our power is 
derived. The light, the chemical emanations, all the rays which that orb sends 
us, are extremely rapid vibrations, analogous to those produced by sound ; 
there is movement, there is force; as soon as it reaches the plant that force is 
absorbed, it disappears, it is extinguished. But no force is extinguished ex- 
cept on the condition of having produced an effect, performed a work which is 
its equivalent. Now the work performed by the light which the leaves absorb 
is decomposing the carbonic acid. So, too, let it not be forgotten, there is 
needed a given amount of force to disunite a given quantity of oxygen and car- 
bon; it is the sun which every hour of the day furnishes it gratuitously. 
If now we place in presence of one another this oxygen and carbon, and, 
by an inverse operation, combine them by burning this carbon, they will pro- 
duce, in uniting anew, all the force which it had been necessary to expend in 
order to separate them; that is to say, all which the sun had furnished. There 
will be heat and light, as experience shows, and there will be force also, which 
may be collected by means of calorific machinery and employed in our service. 
And we shall do well to reflect that it is the sun which has prepared for us 
that heat, that light, and that foree; which has furnished to the carboniferous 
forests at an epoch when man as yet: was not, what man recovers and disposes 
of to-day. 
And what is true of our inanimate furnaces will! be found to be repeated in 
those living furnaces which we call animals. They likewise burn organic 
material, produce heat which elevates their temperature, and develop force and 
movement: a force which they do not create, which they owe to that very com- 
