273 SIXTH REPORT — 183C. 



and diastolic actions were quite normal. The second sound, for 

 example, was suppressed by 



1. Pressure on the roots of the arteries. 



2. By hooking up a valve of each set of sigmoids. 



3. By suspending the heart out of the chest, 



4. By inverting the auricles, &c. (see Exp. passim), the first 

 sound and alternate ventricular actions continuing unaffected in 

 any material degree in each case. Such facts, of which there 

 are many in the account of the experiments, seemed to the Com- 

 mittee quite incompatible with any other hypothesis respecting 

 the second sound than the last, viz. that which refers it to the 

 action of the semilunar valves. Besides, several of those hy- 

 potheses appeared liable to the weighty preliminary objection 

 that they are wholly arbitrary, and without any foundation, so 

 far as the Committee have been able to ascertain, in accurate 

 observations or experiments. Under those impressions the 

 Committee think it best to proceed at once to state the facts 

 which in their opinion tend to establish the action of the sigmoid 

 valves to be the cause of the normal second sound. In this some 

 repetition perhaps may be necessary, but will, it is hoped, be ex- 

 cused. 



The following experiments were made mth especial reference 

 to the mechanism of the second sound. 



1. Pressure with the finger and thumb was exerted on the ar- 

 teries close to the sigmoid valves, so as to flatten the tubes a 

 little, and the second sound, previously clear, and in every re- 

 spect normal, was immediately suppressed, and a bellows mur- 

 mur was heard instead : this murmur ceased, and the normal 

 sound returned instantly on the removal of the fingers. Eperi- 

 ments 7 and 10. 



2. A degree of pressure sufficient, it was conceived, to change, 

 but very slightly, the shapes of the vessels, gave to the finger 

 sensations of currents moving in opposite directions ; the one 

 current more striking, and coinciding with the systole ; the other 

 less forcible and synchronous with the diastole, and ending 

 suddenly by a sensation of flapping or jerking. Experiment 14. 



3. The fingers being applied gently to the region of the sig- 

 moid valves, and the ear-tube applied to the heart, the flapping 

 sound was heard, and a sensation of a gentle tap was felt by the 

 finger, in coincidence with the diastole and second sound. Ex- 

 periments 10 and 14. 



4. One valve of each set of sigmoids was hooked up in each ar- 

 tery successively, and the jerking motion invariably ceased, with 

 one apparent exception only, and continued suppressed in the 



i 



