d. Animal heat, moreover, is the same in kind
as the heat of a fire, being produced by the same chemical process. Animal
motion, too, is as directly derived from the food of the animal as the
motion of Trevethyck's walking engine from the fuel in its furnace. As
regards matter, the animal body creates nothing; as regards force, it
creates nothing. Which of you by taking thought can add one cubit to his
stature? All that has been said, then, regarding the plant may be restated
with regard to the animal. Every particle that enters into the composition
of a muscle, a nerve, or a bone has been placed in its position by
molecular force. And, unless the existence of law in these matters is
denied, and the element of caprice introduced, we must conclude that,
given the relation of any molecule of the body to its environment, its
position in the body might be determined mathematically. Our difficulty is
not with the _quality_ of the problem, but with its _complexity_; and this
difficulty might be met by the simple expansion of the faculties which we
now possess. Given this expansion, with the necessary data, and the chick
might be deduced as rigorously and as logically from the egg as the
existence of Neptune was deduced from the disturbances of Uranus, or as
conical refraction was deduced from the undulatory theory of light.

You see, I am not mincing matters, but avowing nakedly what many
scientific thinkers more or less distinctively believe. The formation of a
crystal, a plant, or an animal is, in their eyes, a purely mechanical
problem, which differs from the problems of ordinary mechanics in the
smallness of the masses and the complexity of the processes involved. Here
you have one half of our dual truth; let us now glance at the other half.
Associated with this wonderful mechanism of the animal body, we have
phenomena no less certain than those of physics, but between which and the
mechanism we discern no necessary connection. A man, for example, can say
_I feel_, _I think_, _I love_; but how does _consciousness_ infuse itself
into the problem? The human brain is said to be the organ of thought and
feeling; when we are hurt, the brain feels it; when we ponder, it is the
brain that thinks; when our passions or affections are excited, it is
through the instrumentality of the brain. Let us endeavor to be a little
more precise here. I hardly imagine that there exists a profound
scientific thinker, who has reflected upon the su