CHAP. XXVin.] THE FORCE OF THE HEART. 361 



of sustaining in a tube fixed in the carotid artery a column of 

 blood 7^ feet high, and calculating the surface of the left ventricle 

 at 15 square inches, he concludes that when it first begins to contract 

 the ventricle supports a pressure of 51'51bs. of blood. And Poiseuille 

 assigns 4 Ibs. 4 oz. as indicating the force which the left ventricle 

 exerts at the moment of its contraction in propelling the blood 

 into the aorta. 



Volkmann combats the grounds upon which Poiseuille' s cal- 

 culation was formed ; and assigns the heart's power as equivalent 

 to the force which sets the stream of blood in motion, and 

 gives it its proper velocity, and also to that which enables it to 

 overcome the obstacles it has to encounter. This latter power is 

 determined by the pressure in the artery, which is found in the 

 mean, in the carotid artery of mammals, to be capable of supporting 

 a column of mercury of 200 millimetres, or about 7 inches ; or a 

 column of blood of 2,700 millimetres (mercury being 13*5 times 

 heavier than blood) ; whilst the former force, taking the actual 

 velocity of the blood in the commencement of the aorta at 400, and 

 in the carotid at 300, would be represented by a column of blood 

 a little more than 8 millimetres in height. Thus it would appear 

 that the force of the heart may be expressed by the following 

 formula 



H=8-2+2700 millim. 



or that it is capable of supporting a column of blood nearly 9 feet 

 in height, which is equivalent to a column of mercury of about 8 

 inches.* 



That the heart's force is extended to the whole arterial system, 

 and must therefore be highly instrumental in maintaining the cir- 

 culation through it, is shewn by the fact, that a considerable pressure 

 is exerted in the various arteries, which can be measured by the 

 ha3madynamometer,or by other instruments. Poiseuille had affirmed 

 that the pressure in all the arteries was the same, a column of mer- 

 cury of the same height being supported by the blood's pressure in 

 all.f This doctrine, however, is at variance with every obvious 



* See the remarks on this subject in the late Dr. Young's Croonian Lecture 

 on the Functions of the Heart and Arteries. Phil. Trans. 1809, and republished 

 in his Introduction to Med. Literature, 1823, p. 607 et seqq. 



t As an example, the pressure in the carotid of a dog, distant 208 millim. from 

 the heart, and that in the humeral artery 303 millim. distant, support a column 

 of mercury of 179 P 04 millimetres. Whence Poiseuille infers, that a particle of 

 blood in the carotid, distant from the heart 208 millim., moves with the same 

 force as a particle in the humeral artery, which has a distance of 303 millim. 



VOL. II. B B 



