WILLIAM HARVEY. 



387 



they moved or not, was a point which could be 

 determined only by experiment. And, for want 

 of sufficiently careful experimentation, Erasistra- 

 tus strayed into a hopelessly misleading path. 

 Observing that the arteries are usually empty of 

 blood after death, he adopted the unlucky hy- 

 pothesis that this is their normal condition, and 

 that during life, ?(|!o, they are filled with air. 

 And it will be observed that it is not improb- 

 able that Erasistratus's discovery of the valves 

 of the heart and of their mechanical action 

 strengthened him in this view. For, as the ar- 

 teria venosa branches out in the lungs, what more 

 likely than that its ultimate ramifications absorb 

 the air which is inspired ; and that this air, 

 passing into the left ventricle, is then pumped all 

 over the body through the aorta, in order to sup- 

 ply the vivifying principle which evidently resides 

 in the air ; or, it may be, of cooling the too great 

 heat of the blood ? How easy to explain the 

 elastic bounding feel of a pulsating artery by the 

 hypothesis that it is full of air. Had Erasistratus 

 only been acquainted with the structure of in- 

 sects, the analogy of their tracheal system would 

 have been a tower of strength to him. There 

 was no prima-facie absurdity in his hypothesis — 

 and experiment was the sole means of demon- 

 strating its truth or falsity. 



More than four hundred years elapsed before 

 the theory of the motion of the blood returned 

 once more to the strait road which leads truth- 

 ward ; and it was brought back by the only pos- 

 sible method, that of experiment, A man of ex- 

 traordinary genius, Claudius Galenus, of Perga- 

 mos, was trained to anatomical and physiological 

 investigation in the great schools of Alexandria, 

 and spent a long life in incessant research, teach- 

 ing, and medical practice. 1 More than one hun- 

 dred and fifty treatises from his pen, on philo- 

 sophical, literary, scientific, and practical topics, 

 are extant ; and there is reason to believe that 

 they constitute not more than a third of his 

 works. No former anatomist had reached his 

 excellence, while he may be regarded as the 

 founder of experimental physiology. And, it is 

 precisely because he was a master of the experi- 

 mental method, that he was able to learn more 

 about the motions of the heart and of the blood 

 than any of his predecessors ; and to leave to 

 posterity a legacy of knowledge, which was not 

 substantially increased for more than thirteen 

 hundred years. 



The conceptions of the structure of the heart 



1 Galen was born in the year 131 a. d., and died in 

 or about the year 201. 



and vessels, of their actions, and of the motion 

 of the blood in them, which Galen entertained, 

 are not stated in a complete shape in any one of 

 his numerous works. But a careful collation of 

 the various passages in which these conceptions 

 are expressed, leaves no doubt upon my mind 

 that Galen's views respecting the structure of the 

 organs concerned were, for the most part, as ac- 

 curate as the means of anatomical analysis at his 

 command permitted ; and that he had exact and 

 consistent, though by no means equally just, 

 notions of the actions of these organs, and of the 

 movements of the blood. 



Starting from the fundamental facts estab- 

 lished by Erasistratus respecting the structure of 

 the heart and the working of its valves, Galen's 

 great service was the proof, by the only evidence 

 which could possess demonstrative value, namely, 

 by that derived from experiments upon living ani- 

 mals, that the arteries are as much full of blood 

 during life as the veins are, and that the left 

 cavity of the heart, like the right, is also filled 

 with blood. 



Galen, moreover, correctly asserted, though 

 the means of investigation at his disposition did 

 not allow him to prove the fact, that the ramifi- 

 cations of the vena arteriosa in the substance of 

 the lungs communicate with those of the artc- 

 ria venosa, by direct, though invisible, passages, 

 which he terms anastomoses ; and that, by means 

 of these communications, a certain portion of the 

 blood of the right ventricle of the heart passes 

 through the lungs into the left ventricle. In fact, 

 Galen is quite clear as to the existence of a cur- 

 rent of blood through the lungs, though not of 

 such a current as we now know traverses them. 

 For, while he believed that a part of the blood of 

 the right ventricle passes through the lungs, and 

 even, as I shall show, described at length the 

 mechanical arrangements by which he supposes 

 this passage to be effected, he considered that 

 the greater part of the blood in the right ventricle 

 passes directly, through certain pores in the sep- 

 tum, into the left ventricle. And this was where 

 Galen got upon his wrong track, without which 

 divergence a man of his scientific insight must in- 

 fallibly have discovered the true character of the 

 pulmonary current, and not improbably have been 

 led to anticipate Harvey. 



But, even in propounding this erroneous hy- 

 pothesis of the porosity of the septum, it is in- 

 teresting to observe with what care Galen dis- 

 tinguishes between observation and speculation. 

 He expressly says that he has never seen the 

 openings which he supposes to exist, and that he 



