requires frequent painful wound dressings, there is a gradual
increase in the acuteness of the pain of the receptors.
This is caused by summation. In a larger sense, the entire behavior
of the individual gives considerable evidence of summation, _e.
g_., in the training of athletes, the rhythmic discharge of muscular
energy at such intervals that the resting stage is not reached
before a new exercise is given results in a gradual ascent
in efficiency until the maximum is reached. This is summation,
and summation plays a large role in the development of both normal
and pathologic phenomena.

We have now pointed out the manner in which at least
a part of the nervous energy of man may be discharged.
The integrative action of the nervous system and the discharge
of nervous energy by phylogenetic association may be illustrated
by their analogy to the action of an electric automobile.
The electric automobile is composed of four principal parts:
The motor and the wheels (the muscular system and the skeleton);
the cells of the battery containing stored electricity
(brain-cells, nervous energy); the controller, which is connected
with the cells by wiring (the receptors and the nerve-fibers);
and an accelerator for increasing the electric discharge
(thyroid gland?). The machine is so constructed that it acts
as a whole for the accomplishment of a single purpose.
When the controller is adjusted for going ahead (adequate stimulus
of a receptor), then the conducting paths (the final common path)
for the accomplishment of that purpose are all open to the flow of
the current from the battery, and the vehicle is integrated to go ahead.
It spends its energy to that end and is closed to all other impulses.
When the controller is set for reverse, by this adequate stimulus