Let us trace out the history of the Horse in another direction. After
a certain time, as the result of sickness or disease, the effect of
accident, or the consequence of old age, sooner or later, the animal
dies. The multitudinous operations of this beautiful mechanism flag in
their performance, the Horse loses its vigour, and after passing
through the curious series of changes comprised in its formation and
preservation, it finally decays, and ends its life by going back into
that inorganic world from which all but an inappreciable fraction of
its substance was derived. Its bones become mere carbonate and
phosphate of lime; the matter of its flesh, and of its other parts,
becomes, in the long run, converted into carbonic acid, into water, and
into ammonia. You will now, perhaps, understand the curious relation
of the animal with the plant, of the organic with the inorganic world,
which is shown in this diagram (Fig. 3).

[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.