The Works of William Harvey M.D. / Translated from the Latin with a life of the author

by William Harvey

Now, if Aristotle understands by the heart that which first appears in the embryo of the chick in ovo, the blood, to wit, with its containing parts—the pulsating vesicles and veins, as one and the same organ, I conceive that he has expressed himself most accurately; for the blood, as it is seen in the egg and the vesicles, is partly similar and partly dissimilar. But if he understands the matter otherwise, what is seen in the egg sufficiently refutes him, inasmuch as the substance of the heart, considered independently of the blood—the ventricular cone—is engendered long afterwards, and continues white without any infusion of blood, until the heart has been fashioned into that form of organ by which the blood is distributed through the whole body. Nor indeed does the heart even then present itself with the structure of a similar and simple part, such as might become a primogenial part, but is seen to be fibrous, fleshy, or muscular, and indeed is obviously what Hippocrates styled it,—a muscle or instrument of motion. But the blood, as it is first perceived, and as it pulsates, included within its vesicle, has as manifestly the constitution which Aristotle held necessary in a principal part. For the blood, whilst it is naturally in the body, has everywhere apparently the same constitution; when extravasated, however, and deprived of its native heat, immediately, like any dissimilar compound, it separates into several parts.

Were the blood destined by nature, however, for the nourishment of the body only, it would have a more similar constitution, like the chyle or the albumen of the egg; or at all events it would be truly one and a single body composed of the parts or juices indicated, like the other humours, such as bile of either kind, and pituita or phlegm, which retain the same form and character without the body, which they showed within their appropriate receptacles;—they undergo no such sudden change as the blood.

Wherefore, the qualities which Aristotle ascribed to a principal part are found associated in the blood; which as a natural body, existing heterogeneously or dissimilarly, is composed of these juices or parts; but as it lives and is a very principal animal part, consisting of these juices mingled together, it is an animated similar part, composed of a body and a vital principle. When this living principle of the blood escapes, however, in consequence of the extinction of the native heat, the primary substance is forthwith corrupted and resolved into the parts of which it was formerly composed; first into cruor, afterwards with red and white parts, those of the red parts that are uppermost being more florid, those that are lowest being black. Of these parts, moreover, some are fibrous and tough, (and these are the uniting medium of the rest,) others ichorous and serous, in which the mass of coagulum is wont to swim. Into such a serum does the blood almost wholly resolve itself at last. But these parts have no existence severally in living blood; it is in that only which has become corrupted and is resolved by death that they are encountered.

Besides the constituents of the blood now indicated, there is yet another which is seen in the blood of the hotter and stronger animals, such as horses, oxen, and men also of ardent constitution. This is seen in blood drawn from the body as it coagulates, in the upper part of the red mass, and bears a perfect resemblance to hartshorn-jelly, or mucilage, or thick white of egg. The vulgar believe this matter to be the pituita; Aristotle designated it the crude and unconcocted portion of the blood.

I have observed that this part of the blood differs both from the others and from the mere serous portion in which the coagulated clot is wont to swim in the basin, and also from the urine which percolates through the kidneys from the blood. Neither is it to be regarded as any more crude or colder portion of the blood, but rather, as I conceive, as a more spiritual part; a conclusion to which I am moved by two motives: first, because it swims above the bright and florid portion—commonly thought to be the arterial blood—as if it were hotter and more highly charged with spirits, and takes possession of the highest place in the disintegration of the blood.

Secondly, in venesection, blood of this kind, which is mostly met with among men of warm temperament, strong and muscular, escapes in a longer stream and with greater force, as if pushed from a syringe, in the same way as we say that the spermatic fluid which is ejected vigorously and to a distance is both more fruitful and full of spirits.

That this mucaginous matter differs greatly from the ichorous or watery part of the blood, which, as if colder than the rest, subsides to the bottom of the basin, appears on two distinct grounds: for the watery and sanious portion is too crude and unconcocted ever to pass into purer and more perfect blood; and the thicker and more fibrous mucus swimming above the clot of the blood itself appears more concoct and better elaborated than this; and so in the resolution or separation of the blood it comes that the mucus occupies the upper place, the sanies the lower; the clot and red parts, however,—both those of a brighter and those of a darker colour,—occupy the middle space.

For it is certain that not only this part, but the whole blood, and indeed the flesh itself—as may be seen in criminals hung in chains—may be reduced to an ichorous sanies; that is to say, become resolved into the matters of which they were composed, like salt into the lixivium from which it had been obtained. In like manner, the blood taken away in any cachexy abounds in serum, and this to such an extent that occasionally scarce any clot is seen—the whole mass of blood forms one sanies. This is observed in leucophlegmatia, and is natural in bloodless animals.

Further, if you take away some blood shortly after a meal, before the second digestion has been completed and the serum has had time to descend by the kidneys, or at the commencement of an attack of intermittent fever, you will find it sanious, inconcoct, and abounding in serum. On the contrary, if you open a vein after fasting, or a copious discharge of urine or sweat, you will find the blood thick, as if without serum, and almost wholly condensed into clot.

And in the same way as in coagulating blood you find a little of the afore-mentioned supernatant mucus, so if you expose the sanies in question, separated from the clot, to a gentle heat over the fire, you will find it to be speedily changed into the mucus; an obvious indication that the water or sanies which separates from the blood in the basin, is perchance a certain element in the urine, but not the urine itself, although in colour and consistence it seems so in fact. The urine is not coagulated or condensed into a fibrous mucus, but rather into a lixivium; the watery or sanious portion of the urine, however, when lightly boiled, does occasionally run into a mucus that swims through the fluid; in the same way, as the mucus in question rendered recrudescent by corruption, liquefies and returns to the state of sanies.