190 PHYSIOLOGY CHAP. 



When water containing a lycopodium suspension is made to 

 circulate through a glass tube of small bore, which alter a short 

 distance continues as one three or four times larger in diameter, it 

 is easy with a lens to see that there is a centripetal eddy at the 

 point where the tube suddenly widens, at which the lycopodium 

 granules at the base of the dilatation become central instead of 

 peripheral in -position, and move towards the axis of the current, 

 where their velocity is greatly accelerated. 



This experiment, which we have demonstrated for over forty 

 years, is well adapted to explain the mechanism of the semilunar 

 valves. Hesse and Krehl showed that in systole the arterial 

 orifices are reduced by the contraction of the longitudinal fibres, 

 which invest the inner wall of the coni arteriosi, to narrow fissures, 

 above which is the marked dilatation formed by the sinus Valsalvae 

 and the bulbi arteriosi. It is clear that the systolic current that 

 Hows out during systole and passes the contracting orifices must 

 make a centripetal vortex in the sinus Valsalvae, which hinders 

 the semilunar valves from opening completely, by tending to 

 throw them into the closed position. So long as the systolic 

 efflux continues, they can only vibrate round the half-opened 

 position ; but as soon as the efflux ceases, the centripetal vortex 

 continues, owing to the force acquired from the blood, and imme- 

 diately flings the valves into the position of closure. This 

 closure, which would only be temporary, becomes permanent from 

 the fact that the column of blood in the artery presses hard 

 against the valves directly diastole commences. 



This mechanism of the opening and closing of the semilunar 

 valves furnishes the best and most rational explanation of the 

 many which have come under discussion. Tigerstedt has explicitly 

 adopted it in a recent synthetic review (1902). But he errone- 

 ously attributes the theory to Krehl, forgetting that it was clearly 

 formulated, and fully developed and illustrated, by Ceradini, in a 

 memoir republished in the German language as early as 1872. 



IV. The mechanism of the auriculo- ventricular valves is 

 essentially similar in type to that of the semiluuars : but con- 

 tains in addition other secondary features, which reinforce, and 

 at the same time complicate, the physiological function of the 

 valves. 



The auriculo-ventricular valves (tricuspid and mitral) consist 

 of tubular membranes, which take origin in the fibrous rings at 

 the base of the ventricles, and divide into three (tricuspid) or two 

 (bicuspid or mitral) flaps (Fig. 58). 



These flaps are united by tendinous cords (chordae tendineae) 



which are attached partially to the free border, partially to the 



inferior surface of the valvular cusps with the pillars formed by 



the larger papillary muscles, or the columnae as they emerge from 



the walls of the ventricle. The mitral valves are more solidly 



