I
Craving is a sign of physiological need. It is a sensory
phenomenon, of which, however, explicit awareness cannot always be
discovered. It is conspicuously noticed in cases of disturbance of the
body secretions, such as occurs in over-function of the thyroid gland.
It is regarded as a crude body-consciousness that something is the
matter. In motorial organisms it causes visible reaction: this expresses
itself in what is termed restlessness. But the unrest may show itself by
a fixation more particularly in the muscles of emotional expression,
although the manifestation is not confined to these; shallow
respirations and restricted amplitude
of movement in limbs and trunk may be observed also.
In cerebrate animals the reaction of the individual is under
the guidance of preceding impressions stored in the pallium
and known as memories; whereas in the animals without a
pallium all reaction is accomplished through stable mechanisms
known as instincts. Both of these types of reaction
are tropisms merely; but the former are labile, conditionable;
whereas the latter cannot be modified. The science of
conditionable reactions of cerebrate animals is called
psychology, and the means by which the reactions are
influenced are called psychogenetic, whether these are healthy
or diseased. It must not be forgotten, however, that the
genesis of a psychological disturbance may be purely somatic,
although the manner in which the reaction shows itself
is contingent mainly upon the features of the individual
which have been derived from previous sensory impressions
and their resultant motor reactions commonly known as
experience. It is the influence of these upon the hereditary
dispositions of the individual which constitute what is
known as "make-up" or character; and it is this which
determines the form which reaction to stimulus must take,
whether the stimulus is purely psychological or somatic.
Now physiological discomfort is an experience universal
at one time of life or another; but the reaction to it is infinite
in variety; and while part of it depends upon the congenital
dispositions which are the common property of humanity, a
larger part is contingent upon the psychogenetic factors
which have stamped the individual.
