478 OF THE CIRCULATION OF THE BLOOD. 



blood takes place into the ventricle at the time of its diastole, causing a rushing 

 sound, analogous to the ordinary first sound, or to some of its modifications. 

 Thus the second sound may come to acquire so completely the character of the 

 first, that it is difficult to distinguish the two in any other way than by the 

 synchronousness of the first with the heart's stroke and with the pulse in the 

 arteries. 1 



509. There seems adequate reason to believe that the whole, or very nearly 

 the whole, of the blood contained in the Ventricles, is discharged from them at 

 each systole ; for the left ventricle is very frequently found quite empty after 

 death ; and if a transverse section be made through the heart, when in a state 

 of well-marked rigor mortis (which may be considered as representing its ordi- 

 nary state of complete contraction), the ventricular cavity is found to be entirely 

 obliterated. 3 From the capacity of the cavity in its state of fullest dilatation, 

 it can scarcely be admitted that more than 3 oz. of blood can be propelled by 

 either ventricle at each systole; 3 and thus, if we estimate the whole amount of 

 blood at 18 Ibs. ( 136), this would require 96 strokes for its passage through 

 either side of the heart; or, reckoning 72 pulsations to a minute, the time elaps- 

 ing before any particle could return to a given point after once passing it (sup- 

 posing it not to be sent elsewhere), would be 1| minute. Between any such 

 estimates, however, and those which are founded upon experimental inquiry into 

 the time required for the passage of substances introduced into the circulating 

 current from one part of the system to another, there is a discrepancy which it 

 is very difficult to reconcile. The earliest of such experiments were those of 

 Hering, 4 who endeavored to ascertain the rapidity of the circulation, by intro- 

 ducing prussiate of potash into one part of the system, and drawing blood from 

 another. He states that he detected this salt, in blood drawn from one of the 

 jugular veins of the Horse, within 20 or 30 seconds after it had been introduced 

 into the other; in which brief space the blood must have been received by the 

 heart, must have been transmitted through the lungs, have returned to the heart 

 again, have been sent through the carotid artery, and have traversed its capil- 

 laries. From experiments of a similar nature upon other veins, he states that 

 the salt passed from the jugular vein into the saphena in twenty seconds ; into 

 the masseteric artery in from 15 to 20 seconds; into the external maxillary 

 artery in from 10 to 25 seconds ; and into the metatarsal artery in from 20 to 40 

 seconds. 5 These experiments have been fully confirmed by those of Poisseuille, 6 



1 On the subject of the Sounds of the Heart, the various treatises on Auscultation by 

 Williams, Blakiston, Hughes, Walshe, Davis, Skoda, Earth and Roger, Weber, and others 

 may be advantageously consulted ; see also Dr. Bellingham's Lectures on Diseases of the 

 Heart, in the " Medical Gazette" for 1850 ; the account of Hamernjk's investigations in 

 the "Edinb. Monthly Journal," Jan., 1849; and those of Kiwisch in the "Brit, and For. 

 Med.-Chir. Rev.," April, 1852. 



2 Kirkes and Paget's "Handbook of Physiology," 2d edit., p. 80. 



3 The total quantity discharged from either ventricle of the human Heart at each systole, 

 is estimated by Valentin at 5.3 oz. ; and by Volkmann at 6.2 oz. ; but these amounts are 

 deduced from calculation of the (supposed) total of the blood, divided by the estimated 

 duration of its passage through the heart, rather than from actual admeasurement. 



4 "Tiedemann's Zeitschrift," vol. iii. p. 85. 



5 Although attempts have been made to invalidate the inference which seems inevitably 

 to flow from these experiments, in regard to the rate of the circulation, by attributing the 

 transmission of the salt to the permeability of the animal tissues, yet it has never been 

 shown that even prussiate of potash (which is probably at least as transmissible through 

 this channel, as any other salt) can be carried from one part to another, with a rapidity at 

 all proportional to this ; and the only mode in which this property can be conceived mate- 

 rially to facilitate the transmission of the salt through the vascular system, would be by 

 allowing it to pass through the septum of the auricles, and thus to make its way from the 

 right to the left side of the heart, without passing through the pulmonary circulation ; yet 

 this it could scarcely do, to the large amount which is evidently transmitted, in so short a time. 



e "Ann. des Sci. Nat.," 1843, Zool., torn, xix., p. 32. 



