476 OF THE CIRCULATION OF THE BLOOD. 



but also (through the imperfect closure of their valves under the same circum- 

 stances) into the large veins. This is proved by the fact, several times observed 

 by. Dr. J. Reid in his experiments upon Asphyxia, &c., that when the action of 

 the right ventricle had ceased from over-distension, he could frequently re-excite 

 it, not merely by puncturing its walls, but by making an opening in the jugular 

 vein. 1 This fact evidently affords an indication of great importance in the treat- 

 ment of Asphyxia ; and it explains the reflux of blood, or venous pulse, which is 

 frequently observed in cases of pulmonary disease, and which, according to Mr. 

 King, always exists even in health, though in a less striking degree. 



505. When the ear is applied over the cardiac region, during the natural 

 movements of the Heart, two successive sounds are heard, each pair of which 

 corresponds with one pulsation ; there is also an interval of silence between each 

 recurrence, and the sound that immediately follows this interval is known as 

 the first sound, the other as the second. The first sound is dull and pro- 

 longed; it is evidently synchronous with the impulse of the Heart against the 

 parietes of the chest, and also with the pulse, as felt near the heart; it must, 

 therefore, be produced during the Ventricular Systole. The second sound, 

 which is short and sharp, 3 follows so immediately upon the conclusion of the 

 first, that it cannot take place during the auricular systole, as some have sup- 

 posed, but must be assigned to the first stage of the ventricular diastole, when 

 the auricles also are dilating. With regard to the relative duration of the two 

 sounds and of the interval, widely different estimates have been formed. Thus 

 Laennec considered the lengths of the periods of sound and silence to be respect- 

 ively 3-4ths and l-4th of the whole interval between one pulse and another ; 

 by Dr. Williams, and by Barth and Roger, the relative lengths of these periods 

 have been estimated at 2-3ds and l-3d; whilst the recent experiments of Volk- 

 mann 3 (made by adjusting two pendulums to vibrate precisely in the two periods) 

 indicate that they are almost precisely equal. 



506. The cause of these sounds, and more especially of the first, has been a 

 subject of much discussion. A number of very distinct actions are taking place 

 during the period of its production ; and each of these has been separately fixed 

 on as competent to produce it. Thus we have (a) the impulse of the heart 

 against the parietes of the chest, (6) the contraction of the muscular walls of 

 the ventricles, (c) the tension of the valves of the auriculo-ventricular orifices, 

 and the backward impulse of the blood against them, (d) the rush of blood 

 through the narrowed orifices of the aorta and pulmonary artery, and (e) the 

 general molecular collision of the particles of the blood amongst each other, and 

 their friction against the walls of the ventricles. Each of these causes has 

 probably some share in the production of the result. 



a. That the first sound is partly due to the impulse, seems proved by the fact, 

 that when the impulse is prevented, by the removal of the portion of the wall 

 of the chest against* which it takes place, the sound is much diminished in 

 intensity ; and also by the circumstance, that, when the ventricles contract with 

 vigour, the greatest intensity of the sound is over the point against which the 

 impulse takes place. Moreover, the prolonged nature of the sound is by no 

 means inconsistent with this view; since the impulse is not a mere stroke, so 

 much as a continued pressure. But that the sound is not entirely due to this 

 cause, is also evident from the fact, that it may still be heard when the heart is 

 contracting out of the body, or when the impulse cannot take place. 



b. That the sound is partly muscular ( 330) would appear from the fact 

 that it may be still perceived after the heart has been removed from the body 



1 Op. cit., Chap. iii. 



2 The difference between these two sounds is well expressed (as Dr. C. J. B. Williams 

 has remarked) by articulating the syllables lubb, dup. 



3 "Die Hamodynamik, nach Versuchen," p. 3G4. 



