304 OF THE CIRCULATION OF THE BLOOD. 



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 in- 

 dication of great importance in the treatment 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. 2 



238. 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 prolonged, and is heard all over the left ventricle with equal intensity; 

 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 supposed, 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 respectively f and J- 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 f and i ; whilst the 

 experiment of Volkmann* (made by adjusting two pendulums to vibrate pre- 

 cisely in the two periods) indicates that they are almost exactly equal. 



239. The causes of the sounds, and more especially of the first, have been 

 the subjects of much discussion. A number of very distinct actions are 

 taking place during the period of the production of the latter; and each of 

 these has been separately fixed on as competent to produce it. Thus we 

 have (1) the impulse of the heart against the parietes of the chest ; ( 2) the 

 contraction of the muscular walls of the ventricles; (3) the rush of blood 

 through the narrowed orifices of the aorta and pulmonary artery ; (4) the 

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

 and their friction against the walls of the ventricles; (5) the sudden col- 

 lision of the stream of blood issuing from the ventricles with the column of 

 blood at rest on the semiluuar valves of the aorta and pulmonary artery; 

 (6) the friction of the heart against the pericardium ; (7) the vibration of 

 the walls of the chest from the sudden rigidity and pressure of the heart ; 

 and (8) the sudden tension of the valves of the auriculo-ventricular orifices. 

 An experiment made by Ur. Halford would seem, at first sight, to permit 

 the first two of the above-mentioned events to be at once dismissed. A large 



1 Phj'siol . Anatom., and Pathol. Researches, chap. iii. 



2 Dr." Herbert Davies (Proceed, lioy. Soc., No. 118, 1870, and pamphlet) maintains 

 that the four chief orifices of the heart are circular in form and constant in area 

 during the entire periods of systole and diastole, and that they bear an exact mathe- 

 matical relationship to each other, expressed by the formula 



Area of tricuspid Area of pulmonic 



Area of mitral Area of aortic 



but his conclusions have been controverted on mathematical grounds by Mr. Trotter, 

 Journ. ol Anal , 1870, p. 298. 



3 The difference bet ween these two sounds is well expressed (as Dr. C. J. B.AVilliams 

 has remarked) by articulating the syllables lubb, diip. 



4 Die Hamodynamik, nach Versuchen, p. 364. 



