reflex action, as the stimulus is conveyed through the mind
and not by the excitement of a peripheral nerve. The whole body
and head are generally at the same time drawn suddenly backwards.
These latter movements, however, can be prevented,
if the danger does not appear to the imagination imminent;
but our reason telling us that there is no danger does not suffice.
I may mention a trifling fact, illustrating this point, and which at
the time amused me. I put my face close to the thick glass-plate
in front of a puff-adder in the Zoological Gardens, with the firm
determination of not starting back if the snake struck at me;
but, as soon as the blow was struck, my resolution went for nothing,
and I jumped a yard or two backwards with astonishing rapidity.
My will and reason were powerless against the imagination of a
danger which had never been experienced.

The violence of a start seems to depend partly on the
vividness of the imagination, and partly on the condition,
either habitual or temporary, of the nervous system.
He who will attend to the starting of his horse, when tired and fresh,
will perceive how perfect is the gradation from a mere glance
at some unexpected object, with a momentary doubt whether it
is dangerous, to a jump so rapid and violent, that the animal
probably could not voluntarily whirl round in so rapid a manner.
The nervous system of a fresh and highly-fed horse sends its
order to the motory system so quickly, that no time is allowed
for him to consider whether or not the danger is real.
After one violent start, when he is excited and the blood
flows freely through his brain, he is very apt to start again;
and so it is, as I have noticed, with young infants.