In his introduction, and by way of clearing the ground, Harvey exposes the views of preceding physiologists, ancient and modern, in regard to the motions of the heart, lungs, and blood, to the state of the arteries, &c.--in short, he gives the accredited physiology of the thoracic viscera, with comments, which prove it a mass of unintelligible and irreconcilable confusion. There is room, therefore, for another interpretation, consonant with reason and with anatomical fact, and susceptible of demonstration by the senses. When he first essayed himself to comprehend the motions of the heart, and to make out the uses of the organ from the dissection of living animals, he found the subject so beset with difficulties that he was almost inclined at one time to say with Fracastorius, that these motions and their purpose could be comprehended by God alone. By degrees, however, by repeating his observations, using greater care, and giving more concentrated attention, he at last discovers a way out of the labyrinth, and a means of explaining simply all that had previously appeared so obscure. Hence the occasion of his writing. Such is the burthen of the proem and first chapter. With Harvey’s admirable work now put in an accessible shape into his hands, we should (did we proceed with an analysis) but anticipate the intelligent reader in the great pleasure he will have in following the author through the different steps of his argument until the conclusion is reached, and the inference presents itself as inevitable, namely, that the blood must circle round and round in one determinate course, in the body as in the lungs, incessantly. For Harvey, it must be here observed, left the doctrine of the circulation as an inference or induction only, not as a sensible demonstration. He adduced certain circumstances, and quoted various anatomical facts which made a continuous transit of the blood from the arteries into the veins, from the veins into the arteries, a necessary consequence; but he never saw this transit; his idea of the way in which it was accomplished was even defective; he had no notion of the one order of sanguiferous vessels ending by uninterrupted continuity, or by an intermediate vascular network, in the other order. This was the demonstration of a later day, and of one who first saw the light in the course of the very year when Harvey’s work on the Heart was published.[29]