32 THE MECHANISM OF THE CIRCULATION. 



them with artificial respiration, and placed them under curari. The 

 committee of the British Association further record, in their investi- 

 gations on the causes of the heart sounds, that the second sound dis- 

 appears when the blood is allowed at each systole to escape not into 

 the arteries, but through openings made in the ventricles. 



The semilunar valves close at that moment when the aortic tension 

 rises the slightest degree higher than the intraventricular pressure ; 

 the closure will therefore be effected gently, and will lead to no sound. 

 In the next moment of time the intraventricular pressure rapidly falls 

 below zero, and the valves will be thrown into tension by the back 

 swing of the blood, which is in its turn occasioned by the elastic 

 rebound of the arteries. The question has been raised as to whether it 

 is the vibration of the valves, or the vibration of the column of blood in 

 the arteries, which produces the second sound. Talma 1 experimented 

 with long glass tubes : to the end of each of these he tied the root of 

 the pulmonary artery with its valves. The tubes after being filled with 

 water were held upright. If, now, the valves were pushed upward with 

 the finger, and then suddenly let go, a sound was heard. If, by varying 

 the height of the fluid columns, the tones in any two tubes were made 

 similar, then, on further varying the height of the column of fluid 



o.i Sec. 



FIG. 21. Tracing of sounds of heart from a case of aortic 

 regurgitation. Einthoven and Geluk. 



in one tube, the tone was found to vary relatively to the height. On 

 these grounds, Talma attributed the sound to the vibration of the 

 column of fluid. These experiments were repeated by Webster, 2 who, 

 in place of the pulmonary valves, employed bladders. He found that 

 if the height of the column of blood were kept constant, the tone varied 

 with the thickness of the bladder. Thus the sound consists of tones 

 produced by the vibration of the membrane, and of others dependent on 

 the vibration of the column of fluid. 



The photographic method of Einthoven makes apparent the exact 

 time relations of the second sound (see Fig. 20). 



It is highly interesting to note the change in the curve of the 

 second sound, resultant on the valves being rendered incompetent. 

 The vibrations are seen to be much more numerous, and to last over a 

 far longer period. In Fig. 21 we see, for the first time recorded by 

 the graphic method, those vibrations which produce a regurgitant 

 murmur. The conclusion reached in regard to the second sound is 

 therefore that it is not simple in origin, but is a sound compounded 

 of two or more tones. These constituent tones arise from vibrations 



1 Arch.f. d. ges. PhysioL, Bonn, 1880, Bd. xxiii. S. 275. 



2 Journ. PhysioL, Cambridge and London, 1882, vol. iii. p. 294. 



