PRAXAGORAS.

PRAXAGORAS. This philosopher appears to have had his knowledge of anatomy from actual inspection of the human body; he is the first who uses the word pulse in the modern sense, and who distinguishes accurately between the two orders of blood-vessels, imagining that the arteries pulsated by a certain inherent power of their own, contained nothing but a spirituous humour, and, taking their rise from the lungs, terminated in the nerves, whose source, with Aristotle, he believed to be the heart. Respiration, he thought, was instituted for the production of the vital spirit. (Conf. Haller, Biblioth. Anat., vol. i., sub voc.)

goras.

HEROPHILUS.

HEROPHILUS was an anatomist of the school of PraxaHis name is still remembered through the title he gave to an intricate portion of the vascular system of the brain, comparing it to a winepressthe Torcular Herophili. He it was who first designated the pulmonary artery and the pulmonary vein by the names they so long retained-Vena arteriosa and Arteria venosa. He seems also to have anticipated every other physiologist by a somewhat careful study of the pulse, which he characterized as full, quick, jerking, rhythmical or the contrary, in different cases. The beat of the artery he concluded correctly must proceed from the action of the heart, but he held erroneously that it was transmitted by the coats of the vessels. Herophilus is said to have dissected the human subject alive. (Haller, ut sup. sub voc.)

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ERASISTRATUS.

ERASISTRATUS. This really distinguished anatomist recognized two principles in the living body-one spirituous, another sanguineous—which were imparted to all its parts by two distinct kinds of vessels, included under the common title of Phlebes. These, he says, intercommunicate or synastomose—a term by which coaptation or juxtaposition, rather than communication by open mouths (although this is not always excluded), appears to have been implied. The blood of the thinner, softer, membranous vessels-the proper blood-vessels, says Erasistratus—is prevented from making its way into the harder tendinous vessels in consequence of their being already replete with vital spirits, or, if it does enter them at any time, disorder and disease are the consequence. When an artery was wounded, the vital spirit, finding a vent, escaped, and then it was that the blood of a neighbouring vein made its way into the artery and flowed out through the wound.

Living in Egypt, Erasistratus had opportunities of learning something of the anatomy of the human

body-nay, he is said to have had criminals presented to him, whom he dissected alive! He was better acquainted with the valves of the heart than any anatomist who had preceded him, and thought that their office was to regulate the flow of the blood and the vital spirits. Prepared by the liver, and brought to the right ventricle of the heart by the vena cava, the blood is passed from thence into the vena arteriosa, which proceeds to the lungs. The left ventricle, again, occupied by the vital spirits imparted to it from the lungs by the arteria venosa, transmits these by the arteria magna to all parts of the body. The purpose of respiration, from what has just been said, is, therefore, to communicate spirit from the inbreathed air to the blood.

Erasistratus certainly apprehended the function of the valves more correctly than Aristotle. Wherever they occur, he says—and the expression leads us to infer that he saw them elsewhere than in the heart-their function is to prevent retrogression of the blood. Referring particularly to those of the heart, the valvula venosa-by which we must understand the tricuspid and mitral valves-he says, give ready access to the ventricles from without, and effectually oppose regurgitation from within. Erasistratus also distinguished more accurately than had been done before between arteries and veins; the arteries alone pulsating by an independent power of their own, whilst the veins were the purely passive channels of

the blood. Elsewhere, however, he ascribes the beating of the heart and arteries to rhythmical efforts of the vital spirit to escape from confinement.

Almost all we know of Erasistratus is derived from the writings of Galen, but the little that has reached us shows him to have been a man in advance of his age, a greater human anatomist than Aristotle, and, if embracing a less extensive field of study, even as particular in describing and interested in accounting for what he saw as the mighty Stagyrite. (Conf. Op. Galeni et Bib. Anat. Halleri, T. I. sub voc.)