same cycle of changes again. The growth of a plant and the
respiration of an animal are dependent on each other.

[Sidenote: The duration of matter and imperishability of force.]
Material particles are thus the vehicles of force. They undergo no
destruction. Chemically speaking, they are eternal. And so, likewise,
force never deteriorates or becomes lessened. It may assume new phases,
but it is always intrinsically unimpaired. The only changes it can
exhibit are those of aspect and of distribution; of aspect, as
electricity, affinity, light, heat; of distribution, as when the
diffused aggregate of many sunbeams is concentrated in one animal form.

It is but little that we know respecting the mutations and distribution
of force in the universe. We cannot tell what becomes of that which has
characterized animal life, though of its perpetuity we may be assured.
It has no more been destroyed than the material particles of which such
animals consist. They have been transmuted into new forms--it has taken
on a new aspect. The sum total of matter in the world is invariable; so,
likewise, is the sum total of force.

[Sidenote: Theory of Averroes.] These conclusions resemble in many
respects those of the philosophy of Averroes, but they are free from the
heresy which led the Lateran Council, under Leo X., to condemn the
doctrines of the great Spanish Mohammedan. The error of Averroes
consisted in this, that he confounded what is here spoken of under the
designation of force with the psychical principle, and erroneously
applied that which is true for animals to the case of man, who is to be
considered as consisting of three essentially distinct parts--a material
body, upon which operate various physical forces, guided and controlled
by an intelligent soul.

In the following paragraphs the distinction here made is brought into
more striking relief.

[Sidenote: Anatomical mode of determining position in the animal
series.] The station of any animal in the organic series may be
determined from the condition of its nervous system. To this observation
man himself is not an exception. Indeed, just views of his position in
the world, of the nature of his intellect and mental operations, can not
be obtained except from the solid support afforded by Anatomy.
[Sidenote: The uselessness of the metaphysical sciences.] The reader has
doubtless remarked that, in the historical sketch of the later progress
of Europe given in this book, I