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 pretty well illustrated among ourselves when we contrast the sexes.  A girl develops in body and mind rapidly, and ceases to grow comparatively early.  A boy’s bodily and mental development is slower, and his growth greater.  At the age when the one is mature, finished, and having all faculties in full play, the other, whose vital energies have been more directed towards increase of size, is relatively incomplete in structure; and shows it in a comparative awkwardness, bodily and mental.  Now this law is true of each separate part of the organism, as well as of the whole.  The abnormally rapid advance of any organ in respect of structure, involves premature arrest of its growth; and this happens with the organ of the mind as certainly as with any other organ.  The brain, which during early years is relatively large in mass but imperfect in structure, will, if required to perform its functions with undue activity, undergo a structural advance greater than is appropriate to its age; but the ultimate effect will be a falling short of the size and power that would else have been attained.  And this is a part-cause—­probably the chief cause—­why precocious children, and youths who up to a certain time were carrying all before them, so often stop short and disappoint the high hopes of their parents.

But these results of over-education, disastrous as they are, are perhaps less disastrous than the effects produced on the health—­the undermined constitution, the enfeebled energies, the morbid feelings.  Recent discoveries in physiology have shown how immense is the influence of the brain over the functions of the body.  Digestion, circulation, and through these all other organic processes, are profoundly affected