to but one stimulus at a time, that is, only one stimulus
occupies the nerve-paths which carry the impulses as a result
of which acts are performed, _i. e_., the final common path.
As soon as a stronger stimulus reaches the brain it dispossesses
whatever other stimulus is then occupying the final common path--
the path of action. The various receptors have a definite order
of precedence over each other (Sherrington). For example, the impulse
from the delicate ticklish points of the skin, whose adequate
stimulus is an insect-like contact, could not successfully compete
for the final common path with the stimulus of a nociceptor.
The stimulus of a fly on the nose would be at once superseded by
the crushing of a finger. In quick succession do the various receptors
(Sherrington) occupy the final common path, but each stimulus is for
the time the sole possessor, hence the nervous system is integrated
(connected) to act as a whole. Each individual at every moment
of life has a limited amount of dischargeable nervous energy.
This energy is at the disposal of any stimulus that obtains possession
of the final common path, and results in the performance of an act.
Each discharge of energy is subtracted from the sum total of stored
energy and, whether the subtractions are made by the excitation
of nociceptors by trauma, by tickling, by fighting, by fear,
by flight, or by the excitation of sexual receptors, by any
of these singly or in combination with others, the sum total of
the expenditure of energy, if large enough, produces exhaustion.
Apparently there is no distinction between that state of exhaustion
which is due to the discharge of nervous energy in response
to trauma and that due to other causes. The manner of the
discharge of energy is specific for each type of stimulation.
On this conception, traumatic shock takes its place as a natural
phenomenon and is divested of its mask of mystery.