When the activity of a ductless gland rises above a certain minimum, its hormones in the blood sensitize, as a photographic plate is sensitized, a group of brain cells, to respond to a message from the outside world, with a definite line of conduct.  There is a registration by the brain cells of the presence of the specific stimulus.  Then there is communication by them with the endocrine organs.  As a result, some of them are moved to further secretion, and others are paralyzed or weakened.  In consequence of changes of concentration in the blood of the various internal secretions, tensions, movements and tumescences, as well as relaxations, inhibitions and detumescences, occur throughout the vegetative system—­the blood vessels, the viscera, the nerves and the muscles.  Each wires to the brain news of the change in it.  In addition, the brain cells themselves are excited or depressed by the new hormones bathing them.  In their final fusion, the commingling vegetative sensations constitute the emotion evolved in the functioning of the instinct.

To lower the new tensions throughout the vegetative system to the normal range, the instinctive action is carried out.  This superficially is regarded as the essence of the instinct.  As a matter of fact, it is only the endpoint of a process, the resultant of a drive to restore equilibrium within the organism.  It may all happen in less time than it takes to tell about it.

The play of an instinct may therefore be analyzed into four processes.  They succeed one another as sensation—­endocrine stimulation—­tension within the vegetative system—­conduct to relieve tension.  The dash is the symbol of a cause and effect relationship.

This equation for an instinct, based upon an analysis of the working of the sex instinct, is the model for the analysis of all instincts, and therefore of all the compounded instincts that all human behaviour may be resolved into.  Conduct, that fascinator of the common gossip and the great novelist alike, normal and abnormal, social and asocial, in all their complexities, even unto the third and fourth generation, the Freudian complexes, is governed therefore by the same laws that determine the movements of the stars and the eruptions of volcanoes.  The most interesting factor in the instinct equation is the endocrine, because that is the one that is most purely chemical.

ENDOCRINE CHARGING OF WISHES

It is the distinction of modern psychology that it has established the wish (craving, need, desire, libido) as the moving force in any psychic process.  The position of the wish in psychology as the force within and behind the instinct may be compared to that of energy in physics, when it was elevated to a central position in the explanation of physical processes in the nineteenth century.  The concept of the charged wish has illuminated all the hidden recesses and rendered audible all the subdued murmurings