THE HEART A DOUBLE PUMP 103 



such through channels must exist. His hearers had not 

 forgotten that a very clever Swiss, named Servetus, had 

 also taught the same doctrine. Harvey boldly proclaimed 

 that the right ventricle was a pump for forcing the blood 

 through the lungs to the left side of the heart, because in 

 no other way could an explanation be given of the con- 

 struction of the chambers, valves, and channels of the 

 right side of the heart. He pinned his faith on the 

 unerring skill with which Nature builds her machines. 

 There were no superfluous parts in her constructions ; 

 every one had its use and meaning. 



There never was a more complete argument than the one 

 which we are now following as Harvey unfolds it. As was 

 the custom at that time, he held a silver-tipped wand in 

 his hand and used it to point out the structures concerned 

 in his discourse. Turning to the left chambers of the 

 heart, he asked his assistant or demonstrator to lay them 

 open. He asked the spectators to note that the mouths 

 by which the vessels of the lungs — the pulmonary veins — 

 opened in the upper or auricular chamber were free and 

 unguarded (fig. 28). On the other hand, the passage from 

 that chamber to the left ventricle was guarded by a stout 

 valve constructed on the same plan as on the right side 

 — except that its funnel-shaped part, hanging within the 

 ventricular cavity, was divided into only two cusps, like a 

 bishop's mitre. The cords of the cusps ended, as in the 

 right side, by being attached to muscular engines pro- 

 jecting from the wall of the cavity and acting as if they 

 were miniature sailors hanging on the stays of wind-filled 

 sails. His audience was willing to agree with him that 

 the passageway between the left auricle and ventricle was 

 competently guarded, and that the blood in the left 

 ventricle could not flow back towards the lungs when 

 that chamber contracted or went into a state of systole. 

 On the other hand, his hearers maintained that although 

 the blood could not go back, yet the sooty fumes brewed 

 in the blood certainly could and did. " Good God ! " 

 exclaimed Harvey, " how can a valve prevent one and 

 not the other ? " The blood having reached the left 



