may cause physiologic exhaustion of and morphologic changes
in the brain-cells. The representation of injury, which is fear,
being elicited by phylogenetic association, may be prevented
by the exclusion of the noci-association or by the administration
of drugs like morphin and scopolamin, which so impair the associational
function of the brain-cells that immunity to fear is established.
Animals whose natural defense is in muscular exertion, among which is man,
may have their dischargeable nervous energy exhausted by fear alone,
or by trauma alone, but most effectively by the combination of both.
What is the mechanism of this discharge of energy? It is the adequate
stimulation of the nociceptors and the physiologic response for the purpose
of self-preservation. According to Sherrington, the nervous system
responds in action as a whole and to but one stimulus at a time.
The integration of the individual as a whole occurs not alone in injury
and fear, but also, though not so markedly, as a result of other
phylogenetic associations, such as those of the chase and procreation.
When adequate stimuli are repeated with such rapidity that the new
stimulus is received before the effect of the previous one has
worn off, a higher maximum effect is produced than is possible
under a single stimulus, however powerful.

Sexual receptors are implanted in the body by natural selection,
and the adequate stimuli excite the nerve-muscular reactions
of conjugation in a manner analogous to the action of the adequate
stimuli of the nociceptors. The specific response of either
the sexual receptors or the nociceptors is at the expense
of the total amount of nervous energy available at the moment.
Likewise in daily labor, which, in the language of evolution,
is the chase, nervous energy is expended. Under the dominance
of fear or injury, however, the integration is most nearly