THE CIRCULATION. 281 



of whidi could reveal its function; in fact, when viewed in a cadaver 

 illusions are very apt to rise. In it the arteries are empty and show 

 a gaping cavity when incised, so that they were thought to contain 

 air or some subtle spirit, the latter taking its origin in the ventricles 

 of the hrain to reach, in some unaccountable manner, the circula- 

 tory system. To them the name artery was given, since the veins 

 alone were believed to be the true blood-vessels. Such was the 

 opinion entertained by men who lived in the fourth and fifth cen- 

 turies before the Christian era. 



In the second century of our era Galen discovered, by means of 

 vivisections, that the arteries contain blood. He even admitted that 

 the arteries communicated with the veins. But, as if to pay his debt 

 to error, he professed that the two hearts are in communication with 

 one another through numerous apertures which riddle the septum 

 that separates the two. For nearly fourteen centuries the opinions 

 of Galen had inviolate authority, when it was finally ascertained by 

 Vesalius that the separating septum was not perforated. It was 

 Michael Servetus who, in a theological work, clearly pointed out the 

 passage of the blood from the right heart to the left through the 

 pulmonary Hood-vessels. His system was true, but not based. upon 

 experiment, since he knew nothing of the heart's force and valves. 



It was in 1628 that William Harvey published his immortal dis- 

 covery of the circulation of the blood. True, a great deal had been 

 suspected and there abounded a perfect chaos of confused and scat- 

 tered facts. He established by numerous and admirably interpreted 

 experiments his doctrine of the two circulations : great and small. 



To-day it would be superfluous to recall all of the arguments 

 which Harvey had to make use of to prop up that doctrine. There- 

 fore there will be stated here only some of his experimental proofs, 

 the interpretation of which appears easy to us in the light of our 

 present knowledge. 



When an artery is opened, said Harvey, the blood issues in 

 unequal jerks, alternately weaker and stronger. The stronger coin- 

 cides with diastole of the artery and consequently with ventricular 

 systole. Also, if an artery of a living animal be cut across, the blood 

 continues to gush by jerks from that end of the vessel still in com-' 

 munication with the heart, whereas it soon ceases to flow from that 

 severed end which is more remote from the central organ. 



When the arm is bound, as for bleeding, the veins swell up 

 below the ligature to become knotty on a level with their valves. If 

 force be attempted to press the blood away from the heart, the 



