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THE BIOLOGY OF ARISTOTLE 41 all voluntary movements throughout the body; though he does not appear to connect them with sensation. At all events, this was the foundation of the celebrated doctrine of the origin of nerves in the heart which was maintained by the followers of Aristotle for hundreds of years. Now one does not recall these misconceptions with the paltry aim, which I have already condemned, of branding as mere errors the imperfect generalizations of the great founder of natural science. It is on account of their historical importance. This point of the relation of the brain and heart was fundamental, and had, I think, a most injurious influence on the progress of physiology. Aristotle’s great services to biology were, first, that he started the investigation; then his great generalization of the unity of the animal kingdom, better appreciated now than ever; and also his marvellous contributions to morphology, which seem to me incomparably more important than his explanations of function, which are largely tinged with metaphysics. In physiology his great achievement was his conception, derived from his studies of the embryo, of the indissoluble connexion of the heart, the blood-vessels, and the blood, by which he kept clear of the liver, that great stumbling-block of the medical anatomists. It was this which Harvey so much appreciated, and one reason which led him to speak of Aristotle with such generous enthusiasm.

Aristotle’s great authority secured through many centuries the vitality of his views as to the rival claims of the heart and brain to be the seat of nervous function and the supreme organ of the body. They were supported chiefly by the philosophers, and opposed by nearly all the medical anatomists. They were the subject of active controversy in the time of Galen. In the Middle Ages they were maintained in opposition to Galen by Averroes, the reviver of the study of Aristotle; and Cesalpino, often spoken of as a forerunner of Harvey, presented them again in the sixteenth century. Nay, about 2000 years after Aristotle’s time, a professor at Padua contemporary with