Besides, supposing even that the action of the brain were not to be suspended from lesions of the red-blooded heart, the animal life would not, on that account, be the less put an end to; because to the exercise of the functions of this life, is attached as a necessary cause, the excitement of its organs by the afflux of blood into them: now this excitement, both here and every where else, depends upon two causes.--1st, On the movement impressed, and 2dly, On the nature of the blood. At present I shall only examine the first mode of influence; the latter will come under our consideration, when we speak of the lungs. Habitual motion is necessary to all the parts of the body alike, is a condition essential to the functions of the muscles, the glands, the vessels, and the membranes, &c. But this movement, which is partly derived from the heart, is very different from that which is communicated by the blood to the brain. The latter organ receives an impulse by which the whole of its mass is visibly raised, an impulse, in the intermission of which the whole of its mass subsides. On the contrary, the interior movement, by which its particles are affected, is scarcely marked at all: and this depends upon the smallness and the delicacy of the vessels by which its substance is penetrated. The contrary of this appearance is observed in the movement occasioned in the other organs by the influx of the blood into them: we see them neither rise nor subside; there is nothing like a general impulse made upon them, because, as I have said, such impulse is lost from the little resistance of the surrounding parts. On the contrary, they are penetrated by vessels of considerable magnitude, which create an intestine motion, oscillations, and impulses adapted to the actions of the tubes, lamellæ, or fibres, of which they are composed. This difference of movement may be easily conceived, by comparing the manner in which the brain on the one hand, and on the other the liver, the spleen, the muscles, or the kidneys receive their blood; indeed it is requisite that the brain should be distinguished from the other organs, in the manner of receiving its impulses, because it is enclosed in a case of bone, and consequently abstracted from the thousand other causes of agitation, to which the other parts of the body are exposed.