organic world, which is shown
in this diagram (Fig. 3).

[Illustration: FIGURE 3. (Diagram showing material relationship of the
Vegetable, Animal and Inorganic Worlds.)]

The plant gathers these inorganic materials together and makes them up
into its own substance. The animal eats the plant and appropriates the
nutritious portions to its own sustenance, rejects and gets rid of the
useless matters; and, finally, the animal itself dies, and its whole
body is decomposed and returned into the inorganic world. There is thus
a constant circulation from one to the other, a continual formation of
organic life from inorganic matters, and as constant a return of the
matter of living bodies to the inorganic world; so that the materials
of which our bodies are composed are largely, in all probability, the
substances which constituted the matter of long extinct creations, but
which have in the interval constituted a part of the inorganic world.

Thus we come to the conclusion, strange at first sight, that the MATTER
constituting the living world is identical with that which forms the
inorganic world. And not less true is it that, remarkable as are the
powers or, in other words, as are the FORCES which are exerted by living
beings, yet all these forces are either identical with those which exist
in the inorganic world, or they are convertible into them; I mean in
just the same sense as the researches of physical philosophers have
shown that heat is convertible into electricity, that electricity is
convertible into magnetism, magnetism into mechanical force or chemical
force, and any one of them with the other, each being measurable in
terms of the other,--even so, I say, that great law is applicable to
the living world. Consider why is the skeleton of this horse capable of
supporting the masses of flesh and the various organs forming the living
body, unless it is because of the action of the same forces of cohesion
which combines together the particles of matter composing this piece of
chalk? What is there in the muscular contractile power of the animal
but the force which is expressible, and which is in a certain sense
convertible, into the force of gravity which it overcomes? Or, if you go
to more hidden processes, in what does the process of digestion differ
from those processes which are carried on in the laboratory of the
chemist? Even if we take the most recondite and most complex operations
of animal life--those of the nervo