he did not see the words, or because the letters were
confusing, or because he had lost memory for the meaning, or because he
had lost the impulse to speak the words, or because he felt unable to
turn his attention, or because the impulse to read aloud was not carried
out by his organism, or because an inner voice told him that it is a sin
to read, or for many similar reasons; and yet each one represents
psychologically an entirely different situation. On the other hand, on
the physical side, the destruction is probably not confined to one
particular spot. Complications have crept over to other places or the
disturbance in one part works as inhibitory influence on other brain
parts, or a tumor may press on a far-removed part, or the disturbance
may be one which cannot be examined with our present microscopic means.
In short, we have always a complex mental situation and a complex
physical one, and to find definite correlations may be possible only by
the comparison of very many cases.

Other methods, however, may supplement the pathological one. The
comparative anatomist shows us that the development of the central
nervous system in the kingdom of animals goes parallel to the
development of the mental functions, and that it is not only a question
of progress along all lines. Any special function of the mind may have
in certain animal groups an especially high development, and we see
certain parts correspondingly developed. The dog has certainly a keener
sense of smell than the man--the part of the brain which is in direct
connection with the olfactory nerve is correspondingly much bulkier in
the dog's brain than in the human organism. Here too, of course,
research may be carried to the subtlest details and the microscope has
to tell the full story. Not the differences in the big structure, but
the microscopical differences in the brain cells of special parts are to
be held responsible. But comparison may not be confined to the various
species of animals; it may refer not less to the various stages of man.
The genetic psychologist knows how the child's mind develops in a
regular rhythm, one mental function after another, how the first days
and first weeks and first months in the infant's life have their
characteristic mental possibilities, and no mental function can be
anticipated there. The new-born child can taste milk, but cannot hear
music. The anatomist shows us that correspondingly only certain nervous
tracts have