And lastly,

4. At what period it may best be made a branch of Education.

Our conclusions on the first of these heads must depend, of course, upon
the nature of the subject-matter of Biology; and I think a few
preliminary considerations will place before you in a clear light the
vast difference which exists between the living bodies with which
Physiological science is concerned, and the remainder of the
universe;--between the phænomena of Number and Space, of Physical and of
Chemical force, on the one hand, and those of Life on the other.

The mathematician, the physicist, and the chemist contemplate things in
a condition of rest; they look upon a state of equilibrium as that to
which all bodies normally tend.

The mathematician does not suppose that a quantity will alter, or that a
given point in space will change its direction with regard to another
point, spontaneously. And it is the same with the physicist. When Newton
saw the apple fall, he concluded at once that the act of falling was not
the result of any power inherent in the apple, but that it was the
result of the action of something else on the apple. In a similar
manner, all physical force is regarded as the disturbance of an
equilibrium to which things tended before its exertion,--to which they
will tend again after its cessation.

The chemist equally regards chemical change in a as the effect of the
action of something external to the body changed. A chemical compound
once formed would persist for ever, if no alteration took place in
surrounding conditions.