ioo THE ENGINES OF THE HUMAN BODY 



and is himself now a physician to the great hospital of the 

 City of London — St Bartholomew's. The lecture-room 

 of the college in which we are to listen to him is small, 

 but filled with a goodly company of learned physicians 

 who are to see the foundation-stones of their most sacred 

 beliefs crumble into dust as the lecturer proceeds. We 

 find him showing the arrangement of valves in the veins ; 

 they are sluice-gates which permit the blood to flow in 

 only one direction — towards the heart. That the blood 

 does flow so can be proved by tying a living vein ; the 

 blood becomes dammed up not on the near side, but on 

 the distant side of the ligature. The blood then is 

 guided towards the right chambers of the heart — the 

 auricle and ventricle. These chambers are opened, and 

 Harvey shows that the passageway between them is 

 guarded by a valve of a curious kind, quite unlike any 

 fitted to ordinary pumps (fig. 28). The valve has to fit an 

 opening or gateway which is always changing in size and 

 shape, and therefore is made up of three parts or cusps 

 which can be made to fit a passage of varying size. The 

 cusps are small triangular sheets or sails of a tough 

 flexible material, with their pointed ends hanging free in 

 the chamber of the ventricle, while their broader ends are 

 fastened to the margin of the auriculo-ventricular passage. 

 The pointed parts of the cusps are tied to the wall of the 

 ventricle by a number of cords — as if the cusps were 

 sails and had been fastened in place by fairy sailors. 

 The chief strings or stays, however, are not fastened 

 directly to the wall of the ventricle, but to finger-like 

 projections which rise up to meet them. These muscular 

 fingers act as engines which can tighten or loosen the 

 cusps or sails according to need. Harvey showed his 

 audience that when blood entered the right ventricle the 

 cusps or sails became bellowed out, and thus blocked the 

 passageway so that the blood could not return to the 

 right auricle. He could not believe, he said, that Nature 

 had set up this elaborate contrivance at the passageway 

 between the right chambers of the heart for no purpose. 

 For him it was a valve, and a valve was a signpost which 



