However difficult these questions may appear, I think it is easy to answer them satisfactorily. By an attentive and deliberate examination, the brain, as well as the spinal marrow (which is nothing more than a prolongation of it) is a kind of mucilage, hardly organized. We distinguish in it only the extremities of the little arteries, which terminate there in great numbers, and carry no blood but a white and nutritive lymph; these small arteries, or lymphatic vessels, when disunited from the brain by maceration, appear in the form of very slender fibres. The nerves, on the contrary, never penetrate the substance of the brain, but only reach the surface of it, but previously to which they lose their solidity and elasticity, and their extremities next the brain are soft, and almost mucilaginous. Whence it appears that the brain, which is nourished by the lymphatic arteries, furnishes in its turn nourishment to the nerves, which we ought to consider as a kind of vegetable substance, that shoots forth from the brain, and is divided into an infinity of branches. The brain is to the nerves what the soil is to plants; the extremities of the nerves are the roots, which, as in every vegetable, are more soft, and tender than the trunk or branches; they contain a ductile matter proper for the growth and nourishment of the tree; and this ductile matter they derive from the substance of the brain, to which the arteries continually direct the lymph necessary for its supply. The brain, therefore, instead of being the seat of sensation, the principle of sentiment, is only an organ of secretion and nutrition, but it is an organ which is highly essential, and without which the nerves could neither grow nor be preserved.