admirable qualities of the blood, have imagined other spirits of an aerial or ethereal nature, or composed of an ethereal or elementary matter, a something more excellent and divine than the innate heat, the immediate instrument of the soul, fitted for all the highest duties. Now their principal motive for this was the consideration that the blood, as composed of elements, could have no power of action beyond these elements or the bodies compounded of them. They have, therefore, feigned or imagined a spirit, different from the ingenerate heat, of celestial origin and nature ; a body of perfect simplicity, most subtile, attenu- ated, mobile, rapid, lucid, ethereal, participant in the qualities of the quintessence. They have not, however, anywhere de- monstrated the actual existence of such a spirit, or that it was superior to the elements in its powers of action, or indeed that it could accomplish more than the blood by itself. We, for our own parts, who use our simple senses in studying natural things, have been unable anywhere to find anything of the sort. Neither are there any cavities for the production and preservation of such spirits, either in fact or presumed by their authors. Fernelius, indeed, has these words : l "He who has not yet completely mastered the matter and state of the inge- nerate heat, let him cast an eye upon the structure of the body, and turn to the arteries, -and contemplate the sinuses of the heart and the ventricles of the brain. When he observes them empty, containing next to no fluid, and yet feels that he must own such parts not made in vain, or without a design, he will soon, I conceive, be brought to conclude that an extremely subtile aura or vapour fills them during the life of the animal, and which, as being of extreme lightness, vanished insensibly when the creature died. It is for the sake of cherishing this aura that by inspiration we take in air, which not only serves for the refrigeration of the body, by a business that might be other- wise accomplished, but further supplies a kind of nourishment." But we maintain that so long as an animal lives, the cavities of the heart and the arteries are filled with blood. We fur- ther believe the ventricles of the brain to be indifferently fitted for any so excellent office, and that they are rather formed for secreting some excrementitious matter. What shall we say,
1 Physiologia, lib. iv, cap. 2.
