NATURAL HISTORY OF SEVENTEENTH CENT. 241 



most strenuous of whom was Riolanus, then professor of anatomy at 

 Paris. Harvey, however, successfully refuted in subsequent publica- 

 tions all the arguments brought against his doctrine, and many years 

 before his death he had the satisfaction of seeing his discovery every- 

 where admitted and publicly explained. Harvey was the author of 

 other valuable treatises scarcely less remarkable for solid reasoning and 

 acute observation. 



The circulation of the blood, as explained and demonstrated by 

 Harvey, is* one of those capital discoveries which completely change 

 or vastly enlarge the conceptions that belong to a whole science. 

 This discovery, which for the first time afforded the means for obtain- 

 ing just views on the nature of physiological processes in general, may 

 be regarded as the very foundation of modern physiology. What men 

 before had learnt of the circulatory apparatus and its functions was 

 but fragmentary or erroneous. Aristotle knew a little about the struc- 

 ture of the heart, and the Alexandrian physician Erasistratus (third cen- 

 tury B.C.) had discovered the valves at the origin of the great vessels. 

 But Erasistratus, finding no blood in the arteries of recently killed 

 animals, concluded that it is the office of these vessels to receive air 

 from the lungs, and distribute it through the body in order to purify 

 the blood. Galen corrected this error by proving experimentally that 

 during life the arteries are filled with blood, and that this blood is, like 

 that which fills the left side of the heart, of a bright red colour. Galen 

 recognized that the function of the lungs is to expose the blood to the 

 action of the air, and he traced the course of the blood from the right 

 side of the heart, through the pulmonary artery, through the lungs 

 themselves, and back to the left side of the heart by the vessel now 

 called the pulmonary vein. He supposed, however, that it was only 

 a small portion of the blood which followed this course, and that the 

 greater part passed immediately from the right to the left side through 

 apertures in the partition between the two ventricles. Another of 

 Galen's errors was to consider that all the veins of the body had their 

 origin in the liver. The fact of the blood in the right side of the heart 

 reaching the left side only by passing through the lungs was not esta- 

 blished until the year A.D. 1559, and by a professor of Padua named 

 REALDUS COLUMBUS. The pulmonary circulation was not, therefore, 

 the discovery of Harvey, whose investigations, however, corroborated 

 the views of the Paduan professor. The originality of Harvey's doc- 

 trine consisted in his maintaining that the blood passes from the left 

 ventricle through the arteries to all parts of the body, and that, follow- 

 ing the ramifications of these vessels, it passes in some way (which 

 Harvey's means of demonstration did not enable him to trace) into 

 the roots of the veins, then into the trunk veins, by which it is con- 

 veyed into the right side of the heart, whence it makes the circuit 

 through the lungs to the left side, and so on. He thus established a 

 truth previously wholly unsuspected, namely, that the same drop of 



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