may
disentangle the confused ideas, for instance, of a dementia praecox, and
thus lead to subtle differential diagnosis.

The psychological laboratory alone can also elaborate the methods of
studying, for instance, the feeble-minded with all the individual
variations. New and ever new methods have been tried; the memory was
tested by reading and repeating figures or letters, or colored papers
were shown or cardboards of different forms or nonsense syllables, and
the powers of remembering were studied. Or the accuracy of arm movements
was examined, or the quickness of understanding associated words, or the
success in planning a complex movement like throwing a ball at a target,
or the tapping of a key in the rhythm of a metronome, or the
discrimination and recognition of the pieces in the game of dominoes and
many another scheme. The laboratory has to analyze the conditions for
such methods and the psychologist has to prepare the means for the use
of the physician, just as the chemist has to prepare the sleeping
powders. In a similar way the laboratory may furnish means to analyze
the mental disturbances by a comparison with the experimental results of
artificial influences, for instance, of over-fatigue or half-sleep, of
drugs or alcohol, of poisons and emotional excitements. The
psychological resolving of the mental symptoms may of course, in the
same way, furnish the diagnosis where the mental variation is only a
distant effect of a bodily ailment. The changes in the emotions, for
instance, may lead to the recognition of a heart disease; lack of
attention may be a hint of the overgrowth of the adenoids; irritability
or apathy or delirious character of the mental behavior may indicate
whether uraemic acid is in the system or an infectious disease: anaemia
and undernutrition may be diagnosed and the psychology of fever demands
too a much closer analysis with the means of the psychological
laboratory than it has received so far.

We have not spoken as yet about those psychological methods which
themselves introduce abnormal mental states like hypnotism, and which
also not seldom are only means for diagnostic purposes. The hypnotic
state may bring to memory forgotten experiences of which the
physiological effects may have lasted in the brain and which may have
brought injury to the psychophysical system. Hypnotic inquiry can thus
lead to the recognition of the first causes in many hysterical states
and where hypnotism i