ACTION OF THE HEART. 479 



and also by those of Mr. Blake j 1 the latter of whom varied them by employing 

 different substances, and took other precautions against sources of fallacy. At 

 an interval of 10 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 5 seconds, he substituted another 

 vessel, which received the blood that flowed during the 5 ensuing seconds ; and 

 the blood that flowed after the 20th second, by which time the action of the 

 Heart had stopped, was received into a third vessel. These different specimens 

 were carefully analyzed. No trace of Baryta could be detected in the blood, 

 which had escaped from the artery between the tenth and the fifteenth second 

 after the injection of the poison; but in that which was drawn between the fif- 

 teenth 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, bear a striking correspondence ; and it may be 

 hence inferred, 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 

 capillaries 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 con- 

 firmation from the fact, that poisons, which act locally on other parts, give the 

 first indications of their operation, in the same period after they have been intro- 

 duced into the Venous circulation. Thus, in the Horse, the time that is required 

 for the blood to pass from the Jugular vein into the capillary terminations of 

 the Coronary arteries, is 16 seconds ; as is shown by the power of Nitrate of 

 Potass to arrest the Heart's action within that time : and Nitrate of Strychnia, 

 injected into a vein, gave the first manifestation of its action on the Spinal Cord, 

 in precisely the same number of seconds. In the Dog, the Heart's action was 

 arrested by the Nitrate of Potass in 11 or 12 seconds ; and the tetanic convul- 

 sions occasioned by Strychnia, also commenced in 12 seconds. In the Fowl, 

 the former period was 6 seconds, and the latter 6; in the Rabbit, the first was 

 4, and the other 4? seconds. From such experiments, it seems evident that 

 the rapidity of the Circulation is underrated, in any estimate that we found upon 

 the capacity of the Heart, and its number of pulsations in a given time ; and 

 it is difficult to see how the two sets of facts are to be reconciled. 



510. The/orce with which the systemic Heart propels the Blood, may be esti- 

 mated in two ways ; either by ascertaining the height of the column of that 

 fluid which its contractile action will support, or by causing the blood to act 

 upon a shorter column of mercury. The former method was the one adopted by 

 Hales, who introduced a long pipe into the Carotid artery of a Horse, and found 

 that the blood would sometimes rise in it to the height of 10 feet. From 

 parallel experiments upon Sheep, Oxen, Dogs, and other animals, and by com- 

 paring the caliber of their respective vessels with that of the Human aorta, 

 Hales concluded, that the usual force of the Heart in Man would sustain a 

 column of blood 7? feet high, the weight of which would be about 4 Ibs. 6 oz. 

 The second method is that which was adopted by Poisseuille ; the result of 

 whose experiments (made with the instrument which he termed the "haemady- 

 namorneter") corresponded very closely with that of Hales, his estimate of the 

 pressure of blood in the aorta being 4 Ibs. 3 oz. [The instrument of Poisseuille, 

 slightly modified by Volkmann, consists of a glass tube bent so as to form a 

 horizontal (B") and two perpendicular (BB') portions. The horizontal portion 

 is capable of being adapted by means of brass tubes of various size to arteries 



' "Edinb. Med. and Surg. Journal," Oct., 1841. 



