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mechanics of the circulation, and in this he practically reached finality. But he naturally pondered over many cognate problems which have continued to exercise physiologists and psychologists to the latest times. It was evidently his intention to deal with these in a separate treatise, for, among other things, in his second letter to Riolan, he says:—
"We also observe the signal influence of the affections of the mind when a timid person is bled and happens to faint. Immediately the flow of blood is arrested, a deadly pallor over-spreads the surface, the limbs stiffen, the ears sing, the eyes are dazzled or blinded. . . And what indeed is more deserving of attention than the fact that in almost every affection, appetite, hope or fear, our body suffers, the countenance changes, and the blood appears to course hither and thither. . . . But here I come upon a field where I might roam freely and give myself up to speculation. And indeed such a flood of light and truth breaks in upon me, occasion offers of explaining so many problems, of resolving so many doubts. . . . that the subject seems almost to demand a separate treatise. And it will be my business in my "Medical Observations" to lay before my
