Notwithstanding the great mobility with which man's organization renders
him susceptible, although exterior as well as interior causes are
continually acting upon him, he does not always feel in a distinct, in a
decided manner, the impulse given to his senses: indeed, he does not
feel it, until it has produced some change, or given some shock to his
brain. Thus, although completely environed by air, he does not feel its
action, until it is so modified, as to strike with a sufficient degree
of force on his organs; to penetrate his skin, through which his brain
is warned of its presence. Thus, during a profound and tranquil sleep,
undisturbed by any dream, man ceases to feel. In short, notwithstanding
the continued motion that agitates his frame, man does not appear to
feel, when this motion acts in a convenient order; he does not perceive
a state of health, but he discovers a state of grief or sickness;
because, in the first, his brain does not receive too lively an impulse,
whilst in the others, his nerves are contracted, shocked, and agitated,
with violent, with disorderly motion: these communicating with his
brain, give notice that some cause acts strongly upon them--impels them
in a manner that bears no analogy with their natural habit: this
constitutes, in him, that peculiar mode of existing which he calls
_grief_.

On the other hand, it sometimes happens that exterior objects produce
very considerable changes on his body, without his perceiving them at
the moment. Often, in the heat of battle, the soldier perceives not that
he is dangerously wounded, because, at the time, the rapidity, the
multiplicity of impetuous motion that assails his brain, does not permit
him to distinguish the particular change a part of his body has
undergone by the wound. In short, when a great number of causes are
simultaneously acting on him with too much vivacity, he sinks under
their accumulated pressure,--he swoons--he loses his senses--he is