mental qualities. Moreover, such mere inclinations and interests
cannot determine the true psychological fitness for a vocation. To
choose a crude illustration, a boy may think with passion of the
vocation of a sailor, and yet may be entirely unfit for it, because
his mind lacks the ability to discriminate red and green. He himself
may never have discovered that he is color-blind, but when he is ready
to turn to the sailor's calling, the examination of his
color-sensitiveness which is demanded may have shown the disturbing
mental deficiency. Similar defects may exist in a boy's attention or
memory, judgment or feeling, thought or imagination, suggestibility or
emotion, and they may remain just as undiscovered as the defect of
color-blindness, which is characteristic of four per cent of the male
population. All such deficiencies may be dangerous in particular
callings. But while the vocation of the ship officer is fortunately
protected nowadays by such a special psychological examination, most
other vocations are unguarded against the entrance of the mentally
unfit individuals.

As the boys and girls grow up without recognizing their psychical
weaknesses, the exceptional strength of one or another mental function
too often remains unnoticed by them as well. They may find out when
they are favored with a special talent for art or music or
scholarship, but they hardly ever know that their attention, or their
memory, or their will, or their intellectual apprehension, or their
sensory perceptions, are unusually developed in a particular
direction; yet such an exceptional mental disposition might be the
cause of special success in certain vocations. But we may abstract
from the extremes of abnormal deficiency and abnormal overdevelopment
in particular functions. Between them we find the broad region of the
average minds with their numberless variations, and these variations