188 PHYSIOLOGY CHAP. 



1. That the position of elastic equilibrium of the senrilunar 

 valves corresponds not witli closure but with half -opening 

 (Fig. 56). 



2. That during the systolic efflux the three sinuses of Valsalva 

 and the bulbus arteriosus dilate, and the seinilunars assume and 

 maintain a half-opened position, with vibration of their free 

 borders, which therefore become blurred and give rise to a muffled 

 sound. 



3. That at the cessation of systole (systolic dead point) the 



valves close rapidly and then reopen, 

 if systole is not followed by diastole. 



4. That when diastole follows v v 

 systole, the valves (which were 

 already closed at the systolic dead 

 point) extend towards the conus 

 arteriosus of the ventricle, forming 

 with their surfaces a tetrahedron, 

 with the point directed upwards, 

 and emit a short sound which is of 

 higher pitch than the preceding. 



From these results it is obvious 

 that the closing of the semilunars 



Fi<;. 50. -Diagrammatic section, life size, j g ^he effect HOt of Commencing 

 across sinus of art. pulmonaris of 

 pig ; constructed by Ceradini from diastole, Dllt Ol the Close OI Systole. 



It is easy to see that no reflux is 

 -possible under these conditions, since . 



.., 



the largest ami 'the least equilateral the valves are already closed at the 



triangle that can be described by the , . . .. -, . *; j ' i 



three outlines (t>, cBh, i>Aa) of the beginning oi diastole, ana when 



sinuses of Valsalva. The circle sur- fVivrkYwn inf^ olaofir* tone-inn rln Vmf 



rounding the smallest triangle repre- thrown intO ClaStlC tension ClO DUt 



sent* the projection of the constric- ^ eep up ^hlS position of closure. 



tion of the artery which divides -W-n-i -i /-N -i > 



the sinoid from the bulbar portion. When, according tO Ceradini S 



method, diastole is imitated by sioxt- 

 in with tbe half-open position of 

 the valves, their closure is obtained 

 by a reflux, and the amount of fluid which under these condi- 

 tions regurgitates from artery to ventricle can be measured. 

 According to Ceradini, this would be considerable, amounting to a 

 seventh part of the flow that leaves the ventricle at systole. This 

 proves the importance of the pre-diastolic closure of the semilunar 

 valves, which normally prevents the loss of a considerable part of 

 the useful effect of the cardiac cycle. 



In repeating the experiment, with Ceradini's apparatus, we 

 found several inconveniences, which we attempted to eliminate by 

 modifications indispensable to the demonstration of the play of the 

 valves before any large audience. Fig. 57 shows this improved 

 apparatus. 



The theoretical explanation of the mechanism of the valves 



