CHAP. XXVIII.] ACTION OF THE HEART. 345 



the regurgitation of a portion of the blood after each systole of the 

 ventricle, a bellows sound becomes generated which usurps the 

 place of the clicking second sound. But the moment the valve is 

 allowed to resume its play, the natural click returns. 



That this is the correct interpretation of the sounds of the heart, 

 is further proved by the observation of the influence of various mor- 

 bid states of that organ upon them. Thus the first sound is modified 

 by whatever increases or weakens the intensity of the ventricular 

 systole, of the impulse, and of the tension of the auriculo-ventricular 

 valves ; and when the latter takes place imperfectly by reason of the 

 insufficiency of the valves to close the orifices, the first sound is 

 accompanied (not replaced) by a bellows sound due to the regurgi- 

 tation of blood from ventricle to auricle. Again, should one or 

 more of the semilunar valves be so injured or altered as to prevent 

 the complete closure of the arterial orifice, at the time of the 

 diastole, the second sound is replaced by a bellows sound, just as 

 in the experiment above detailed. 



The regular succession of the two sounds and the pause, bearing 

 to each other the relative duration already mentioned, constitutes 

 the rhythm of the heart."* Sometimes the pause lasts for a much 

 longer period than a fourth of the whole, for as long or longer than 

 would suffice for the development of the other two sounds. Under 

 these circumstances the heart is said to intermit, and its rhythm 

 is interrupted. 



At every systole of the heart an impulse is felt in all the large 

 arteries of the body, which is synchronous with the contraction of 

 the ventricles, or so nearly that the difference is inappreciable ex- 

 cept in very distant arteries as those of the tarsus. This impulse 

 in the arteries constitutes the pulse which will be fully described 

 by and by (p. 353), and which, from its general accordance with 

 the heart's action, affords the readiest means of judging of the 

 heart's rhythm, and counting the frequency of its action. 



When the rhythm of the heart is regular, this succession of first 

 and second sound (systole and diastole) and pause may be heard 

 a certain number of times in a minute in each individual, and by a 

 series of observations, the scale may be formed shewing the average 

 frequency of the heart's action at different periods of life in man. 

 This is shewn in the following table, which is that formed by our 

 able friend and colleague, Dr. Guy, from a comparison of numerous 

 observations.f 



* Some observers admit the existence of a short pause after the first sound, 

 f Art. Pulse, Cycl. Anat. and Phys. 



VOL, IT. A A 



