THE MOTION OF THE BLOOD. 179 



projection, much less the obstacles to the powers of the heart, 

 can be accurately determined, &c. 



" A rough calculation may be made by taking every probable 

 conjecture together : v. c., if the mean mass of the blood is con- 

 sidered as 10 pounds, or 120 ounces; the pulsations 75 in a 

 minute, or 4500 in an hour ; and the quantity of blood expelled 

 from the left ventricle at each contraction, as 2 ounces ; it 

 follows that all the blood must pass through the heart 75 times 

 every hour. 



" The impetus of the blood passing from the heart may be 

 conceived by the violence and altitude of the stream projected 

 from a large wounded artery situated near it. I have seen the 

 blood driven at first to the distance of above five feet from the 

 carotid of an adult and robust man. 



" This wonderful, and, while life remains, constant, strength of 

 the heart, is universally allowed to depend upon its irritability, 

 in which it very far surpasses, especially as to duration^, every 

 other muscular part. 6 



" That the parietes of the cavities are excited to contraction 

 by the stimulus of the blood, is proved by the experiment of 

 Haller, who lengthened, at pleasure, the motion of either side of 

 the heart, by affording it the stimulus of the blood for a longer 

 period than the other." f 



c " The experiments of Hales, in which the blood was received into very long 

 glass tubes fixed to the arteries of living animals, and the length of its projection 

 measured, are indeed beautiful, like every thing done by this philosopher, who 

 was calculated by nature for such enquiries. But, if the force of the heart is to 

 be estimated in this way, we must take into account the pressure of the column 

 of blood contained in the tube and gravitating upon the left ventricle. 



" The result of Hales's calculations was, that, the blood being projected from 

 the human carotid to the height of seven feet and a half, and the surface of the 

 left ventricle being fifteen square inches, a column of blood, weighing 51 -5 Ibs. 

 was incumbent upon the ventricle, and overcome by its systole. Statical JEssays, 

 vol. ii. p. 40. London, 1733. 8vo." 



d " Thus, to say nothing of the phenomena so frequently observed in the cold- 

 blooded amphibia and fishes, I lately found the heart of the chick to beat for 

 twelve hours, in an egg, on the fourth day of incubation." 



e " Consult Fontana, who treats of this prerogative of the heart minutely in 

 his Ricerche sopra la Fisica animate, and limits it too much. Haller answered 

 him in the Literary Index of Gottingen." 



f " See Haller on the motion of the heart from stimulus. Comment. Soc. Scient. 

 Gottingens. torn. i. 



G. E. Remus, Experimenta circa circulat. sanguin, instituta. Gotting. 17 

 4to. p. 14." 



N 4 



