system any monopoly of the function, even when it is as highly
developed as in Man. . . . Just as the direct excitability of the
nervous system has progressed in the history of the race, so has its
capacity for receiving imprints; but neither susceptibility nor
retentiveness is its monopoly; and, indeed, retentiveness seems
inseparable from susceptibility in living matter."


Semen here takes the instance of stimulus and imprint actions
affecting the nervous system of a dog


"who has up till now never experienced aught but kindness from the
Lord of Creation, and then one day that he is out alone is pelted
with stones by a boy. . . . Here he is affected at once by two sets
of stimuli: (1) the optic stimulus of seeing the boy stoop for
stones and throw them, and (2) the skin stimulus of the pain felt
when they hit him. Here both stimuli leave their imprints; and the
organism is permanently changed in relation to the recurrence of the
stimuli. Hitherto the sight of a human figure quickly stooping had
produced no constant special reaction. Now the reaction is constant,
and may remain so till death. . . . The dog tucks in its tail
between its legs and takes flight, often with a howl [as of] pain."

"Here we gain on one side a deeper insight into the imprint action of
stimuli. It reposes on the lasting change in the conditions of the
living matter, so that the repetition of the immediate or synchronous
reaction to its first stimulus (in this case the stooping of the boy,
the flying stones, and the pain on the ribs), no longer demands, as
in the original state of indifference, the full stimulus a, but may