CHAP. XXVIII.] THE FORCE OF THE HEART. 359 



and the blood rose, after the successive bleedings, to seven, six, five, 

 four, and at length to two feet four inches, 



In a second experiment, exactly the same, excepting that it was 

 made on a horse of more vigour than the subject of the previous 

 one, the blood rose to nine feet eight inches, and fell subsequently, 

 after successive bleedings, in the same manner as in the first experi- 

 ment. A third experiment made upon a mare, consisted in fixing 

 the brass pipe into the carotid artery towards the heart, and to 

 that the windpipe of a goose, on account of its pliancy, and to the 

 other end of that a glass tube, twelve feet nine inches long. The 

 blood rose in the tube to nine feet six inches, and behaved, in all 

 respects, much in the same way as in the former experiments. 

 And afterwards, Hales experimented in the same way on the sheep, 

 the deer, the dog, with results essentially similar, but varying with 

 the size and general power of the animal. 



Hales estimated the force of the left ventricle of the heart at the 

 moment of its systole, by multiplying the area of its inner surface 

 into the height of the column of blood in the tube, which it was 

 capable of sustaining, calculating also the absolute weight of the 

 quantity of blood which formed that column. From these data he 

 concluded that the contraction of the left ventricle of the horse's 

 heart was capable of sustaining a weight of 1131bs. ; that of the 

 sheep, 36-56 Ibs. ; that of the dog, 33'61 Ibs., when the animal 

 weighed 52 Ibs., and 19-8 and ll'l Ibs., in dogs weighing respec- 

 tively 24 Ibs. and 18 Ibs. 



Poiseuille improved upon the method of Hales' s experiments, and 

 obviated some objections to them. He employed an instrument 

 which he called the hcemadynamometer. (Fig. 201.) This consisted 

 of a glass tube bent so as to form a horizontal (B") and two perpen- 

 dicular (BB') portions. The horizontal portion is capable of being 

 adapted by means of brass tubes of various size to arteries or 

 veins, however different in calibre. The tube is attached to a 

 board (AA'), on which a scale is marked. To use it mercury is 

 poured into the perpendicular branches of the tube, and will, of 

 course, stand at the same height in each when the instrument is 

 kept in the perpendicular. 



In order to prevent the coagulation of the blood, which, by causing 

 it to adhere to the sides of the tube would complicate the experi- 

 ment (a point not provided against in Hales's experiments) a 

 quantity of a strong solution of carbonate of soda is poured into 

 the horizontal branch, and will therefore rest upon the column of 

 mercury in the nearest vertical branch. 



