of different animals differs in several ways ; in one it is more serous and thinner, a kind of ichor or sanies, as in insect s, and the colder and less perfect animals ; in another it is thicker, more fibrous, and earthy, as in the wild boar, bull, ass, &c. In some where the constitution is distempered, the blood is of a blacker hue ; in others it is bright, pure, and florid, as in birds, and the human subject especially.
Whence, it appears, that in the opinion of the physicians, as well as of Aristotle, the blood consists of several parts, in some sort of the same description, according to the views of each. Medical men, indeed, only pay attention to human blood, taken in phlebotomy and contained in cups and coagulated. But Aristotle took a view of the blood of animals generally, or of the fluid which is analogous to it. And I, omitting all points of controversy, and passing by any discussion of the incon- veniences that waii upon the opinions of writers in general, shall here touch lightly upon the points that all are agreed in, that can be apprehended by the senses, and that pertain more especially to our subject ; intending, however, to treat of every- thing at length elsewhere.
Although the blood be, as I have said, a portion of the body, the primogenial and principal part, indeed, still, if it be considered in its mass, and as it presents itself in the veins, there is nothing to hinder us from believing that it con- tains and concocts nourishment within itself, which it applies to all the other parts of the body. With the matter so con- sidered, we can understand how it should both nourish and be nourished, and how it should be both the matter and the effi- cient cause of the body, and have the natural constitution which Aristotle held necessary in a primogenial part, viz. that it should be partly of similar, partly of dissimilar constitution ; for he says, " As it was requisite for the sake of sensation that there should be similar members in animal bodies, and as the faculty of perceiving, the faculty of moving, and the faculty of nourishing, are all contained in the same member (viz. the primogenate particle), it follows necessarily that this member, which originally contains inherent principles of the above kind, be extant both simply, that it may be capable of sensation of every description, and dissimilarly, that it may move and act. Wherefore, in the tribes that have blood, the heart is held to
