ACTION OF THE HEART. 553 



valves do not close properly; and a reflux of blood is permitted, not only into the Auricle, 

 but also (through the imperfect closure of their valves under the same circumstances), into 

 the large veins. This is proved by the fact, several times observed by Dr. J. Reid, in his 

 experiments upon Asphyxia, &e., 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. This fact evidently affords an indication of great 

 importance in the treatment of Asphyxia ; and it explains the reflux of blood, or venous 

 piilxf, which is frequently observed in cases of pulmonary disease, and which, according to 

 JVIr. King, always exists, though in a less striking degree. 



724. It is not quite certain whether the Ventricles empty themselves com- 

 pletely at each contraction ; but it seems probable that the blood which they 

 contain, is not entirely forced into the arteries. The quantity which is pro- 

 pelled by each Ventricle, at every stroke, may be estimated, therefore, at from 

 1* oz. to 2 oz. If we adopt the lower of these numbers, we shall find that, 

 reckoning 75 pulsations of the Heart to a minute, 112 oz., or 7 Ibs., of blood 

 pass through each ventricle in that time; and, on the higher estimate, 150 

 oz., or 9 Ibs. 6 oz., would pass through in the same period. Now the whole 

 quantity of blood contained in the human body, according to the estimate of 

 Haller (which is considered by Dr. Allen Thomson to be near the truth), is 

 about one-fifth of the weight of the body, or 28 Ibs. in a person weighing 

 140 Ibs.* This quantity would pass through the Heart, therefore, in four 

 minutes, on the lower of the two preceding estimates, or in three minutes on 

 the higher; and would circulate afresh, fifteen or twenty times in an hour. It 

 Avould appear, however, that this estimate of the rapidity of the circulation is 

 very far from the truth; for recent experiments have shown, that substances 

 introduced into the Venous circulation, may be detected in the remotest parts 

 of the Arterial circulation, even in animals larger than Man, in less than half 

 a minute. The earliest of such experiments were those of Hering,t who en- 

 deavoured to ascertain the rapidity of the circulation, by introducing 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 ca- 

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

 that the salt passed from the Jugular vein into the Saphena in 20 seconds ; 

 into the Masseteric artery in from 15 to 20 seconds ; into the External Max- 

 illary artery in from 10 to 25 seconds ; and into the Metatarsal artery in from 

 20 to 40 seconds. An attempt has 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 permea- 

 bility of the animal tissues ;J but it has never been shown, that even Prussiate 

 of Potash (which is probably more transmissible through this channel than 

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

 proportional to this. The only mode in which this property can be con- 

 ceived materially 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 ; and this it could scarcely do, to 

 the large amount which is evidently transmitted, in so short a time. 



725. The experiments of Hering have been recently fully confirmed by 



Valentin's estimate, founded upon different data, closely corresponds with this. 

 [ Tiedemann's Zeitschrift, vol. iii. p. 85. 

 j See Dr. Allen Thomson, foe. tit. 



47 



