in equilibrium, the smallest touching each other, are active in their motion, communicating reciprocally, alternately and in succession, the impression, oscillations, and shocks they receive; in such a composition, it is not surprising that the slightest impulse propagates itself with celerity; that the shocks excited in its remotest parts, make themselves quickly felt in the brain, whose delicate texture renders it susceptible of being itself very easily modified. Air, fire, water, agents the most inconstant, possessing the most rapid motion, circulate continually in the fibres, incessantly penetrate the nerves: without doubt these contribute to that incredible celerity with which the brain is acquainted with what passes at the extremities of the body.
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
