PLATO.

PLATO, the great idealist, has not much in his voluminous writings on the subject that engages us. In the

Timæus," however, he speaks of the heart as the fountain of the blood, and as giving origin to its containing vessels-éßes, a word by which both arteries and veins are designated. The heart, he says, erroneously, has three ventricles; but concludes, correctly, that it is the organ which sets the blood in motion a statement strangely misunderstood or neglected by so many who came after him. He is also the first to call the great artery of the body by the name it still retains-Aorta; and there is a short sentence in connection with what is said of this vessel which must not be passed unnoticed, for it has led to the assumption that Plato was actually acquainted with the circulation of the blood. The blood," he says, "is forcibly carried round to all the members— τὸ ἄιμα κατὰ πάντα τὰ μέλα σφοδρῶς περιφέρεσθαι;” words notable enough when interpreted by the light of the present day, but that could hardly have had the meaning to their writer which has lately been connected with

them, as they certainly had no such sense to the long ages that came after him. The σφοδρώς περιφέρεσθαι however, seems to imply propulsion from the heart; but this, although I believe it influenced Cæsalpinus, was neglected by almost all the rest of Plato's successors until the days of Harvey.

ARISTOTLE.

ARISTOTLE prototype of the man of science of the modern world-the scholar of Plato, was not likely to pass the structure and action of the heart without particular notice, or the important part played by the blood in the animal economy. We find Aristotle accordingly speaking of the heart as the source as well as the reservoir of the blood. Alone, of all the viscera, he says, does the heart contain blood. Everywhere else it is included in vessels-péßes, the name by which, like Plato, he designates both veins and arteries. He distinguishes between the two orders of vessels, however, and says truly that he thinks they are severally complementary, each existing for the sake of the other. (De Respir., cap. ix.)

The heart is further spoken of by Aristotle as the seat and source of the native heat; and the end and object of respiration, with which he holds the beating of the heart to be intimately connected, is to temper or keep the heat of the heart, tending ever towards excess, within proper bounds. "The hotter the animal," says the Stagyrite, "the more vigorously

must it breathe, in order the more effectually to subdue the heat; whence the larger development of the lungs in quadrupeds and birds than in amphibious animals.” The reasons why warm-blooded animals die in water and fishes in air, he thinks, is due to their hearts not being adequately cooled by the inbreathed air in the one case, by the water passed over their gills in the other. (Ibid., cap. xix.)

The air of the atmosphere, held indispensable to the engenderment of the vital spirit, was received from the ramifications of the trachea in the lungs, by contact and insudation, not by any direct communication through open mouths between the bronchial tubes and the blood-vessels.

The pulsation of the heart depended on a sudden expansion or puffing up of the material supplied for the elaboration of the blood by the food digested in the stomach. Coming into contact with the heart as focus of the innate heat, each fresh afflux of nutrient fluid dilating, caused a beat, and as the supply was continuous, so was the pulse without intermission. (Ibid., cap. xx.)

The arteries pulsated synchronously with their source, and the blood flowed alternately from the vessels to the heart, from the heart to the vessels; the valves at the orifices of these regulating the current, and being so disposed that whilst one motion of the heart opened one set and closed another, a second motion of the organ shut those that

had been opened and opened those that had been shut.

In the course of the numerous dissections of the lower animals he performed, and following up what he had said on the cause of the heart's action, Aristotle appears to have observed the lacteal vessels of the mesentery, tending, as he concluded, from the intestines to the vena cava and aorta. Likening them to what is seen in plants, he says: "Even as plants draw nourishment by their roots from the ground, so do animals derive nutriment from the stomach and intestines, these standing to them in lieu of the earth, and having veins in the guise of roots implanted in their substance." (De Part. Animal, lib. iv., cap. 4.)

Singularly enough, when we think of him as the practical anatomist, Aristotle is generally understood as saying that the nerves are derived from the heartled to the conclusion, it may be, by current notions of the heart being the seat or source of the affections, emotions, and passions.