370 OF THE CIRCULATION OF BLOOD. 



It would 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,* who 

 endeavoured to ascertain the rapidity of the circulation, by introducing Prus- 

 siate 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 capillaries. From experiments of a similar nature upon other veins, he 

 states that the salt passed from the Jugular vein into the Saphena in 20 se- 

 conds; 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. 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 ;t 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 conceived 

 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. 



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

 those of Mr. Blake,J who varied them by employing different substances, and 

 took other precautions against sources of fallacy. Ten seconds after having 

 injected a solution of Nitrate of Baryta into the Jugular vein of a horse, he 

 drew blood from the Carotid artery of the opposite side ; after allowing this to 

 flow for five seconds, he substituted another vessel, which received the blood 

 that flowed during the five ensuing seconds ; and the blood that flowed after 

 the twentieth second, by which time the action of the Heart had stopped, was 

 received into a third vessel. These different specimens were carefully ana- 

 lyzed. No trace of Baryta could be detected in the blood which had escaped 

 from the artery between the tenth and fifteenth second after the injection of 

 the poison; but in that which was drawn between the fifteenth and the 

 twentieth second, the salt was found to be present and in greater abundance 

 than in the blood which had subsequently flowed. Moreover, the coincidence 

 between the cessation of the Heart's action, and the diffusion of the salt through 

 the arterial blood, bears a striking correspondence ; and it may be hence in- 

 ferred that the arrestment of its muscular movement is due to the effect of this 

 agent upon its tissue, when immediately operating upon it through the capil- 

 laries of the coronary artery. This conclusion is borne out by a variety of 

 other experiments ; which show that the time of the agency of other poisons, 

 that suddenly check the Heart's action (which is the especial property of 

 mineral poisons), nearly coincides, in different animals, with that which is 

 required to convey them into the Arterial capillaries. And it seems to derive 

 full confirmation from the fact that poisons which act locally on other parts, 



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

 f See Dr. Allen Thomson, Joe. tit. 



* Edinb. Med. and Surg. Journal, Oct., 1841. 



