eeds that which Nature
has provided for; the expenditure for other purposes falls below what it
should have been; and evils of one kind or other are inevitably
entailed. Let us briefly consider these evils.

Supposing the over-activity of brain to exceed the normal activity only
in a moderate degree, there will be nothing more than some slight
reaction on the development of the body: the stature falling a little
below that which it would else have reached; or the bulk being less than
it would have been; or the quality of tissue not being so good. One or
more of these effects must necessarily occur. The extra quantity of
blood supplied to the brain during mental exertion, and during the
subsequent period in which the waste of cerebral substance is being made
good, is blood that would else have been circulating through the limbs
and viscera; and the growth or repair for which that blood would have
supplied materials, is lost. The physical reaction being certain, the
question is, whether the gain resulting from the extra culture is
equivalent to the loss?--whether defect of bodily growth, or the want of
that structural perfection which gives vigour and endurance, is
compensated by the additional knowledge acquired?

When the excess of mental exertion is greater, there follow results far
more serious; telling not only against bodily perfection, but against
the perfection of the brain itself. It is a physiological law, first
pointed out by M. Isidore St. Hilaire, and to which attention has been
drawn by Mr. Lewes in his essay on "Dwarfs and Giants," that there is an
antagonism between _growth_ and _development_. By growth, as used in
this antithetical sense, is to be understood _increase of size_; by
development, _increase of structure_. And the law is, that great
activity in either of these processes involves retardation or arrest of
the other. A familiar example is furnished by the cases of the
caterpillar and the chrysalis. In the caterpillar there is extremely
rapid augmentation of bulk; but the structure is scarcely at all more
complex when the caterpillar is full-grown than when it is small. In the
chrysalis the bulk does not increase; on the contrary, weight is lost
during this stage of the creature's life; but the elaboration of a more
complex structure goes on with great activity. The antagonism, here so
clear, is less traceable in higher creatures, because the two processes
are carried on together. But we see it p