324 



CIRCULATION OF BLOOD. 



LECT. XVII. 



Fig. 25. 



has been the case with respect to the investigation of the 

 force with which the left ventricle contracts. Borelli, 

 Bernouilli, and Keil, obtained 

 numbers which differ very con- 

 siderably from each other. 

 Thus, Borelli estimates the 

 force of the heart as equivalent 

 to that of 180,000 pounds; 

 while Keil, on the contrary, 

 calculates it at only 5 ounces. 



Hales was also the first who 

 made accurate experiments for 

 measuring the pressure of the 

 blood in the arteries ; but it is 

 to Poiseuille that we are in- 

 debted for the most complete 

 investigation of this subject. I 

 shall confine myself to an ex- 

 position of his principal conclu- 

 sions. 



The hffimo-dynamometer of 

 Poiseuille consists of a kind of 

 glass manometer, whose short, 



tamo-dynamometer of Poiseuille. horizontal arm is placed in a 



rent glass tube, filled with mereury . . l 



The horizon- brass tube, which is afterwards 



Haem 



A bent glai 

 in the lower part, e 



tai part b, is provided with a brass i ntroc ] ucec i i nto the artery of the 



head, which fits into the artery. A i T j 



small quantity of a solution of the living animal. In order to pre- 



carbonate of soda is interposed be- yent ^ coagu ] at i on o f the 

 tween the mercury and the blood, to 



prevent its coagulation. When the blood, which obstructs the por- 

 blood presses on the fluid in the hori- fiQ of the tube Situated betWCCn 

 zontal limb, the tise of the mercury 



towards c, measured from the level to the artery and the column of 



which it has fallen towards a, gives mer( , Poiseuille first fills 



the pressure under which the blood 7 



moves. this with a solution of carbonate 



of soda. We then see the column of mercury in the long 

 vertical arm rise, and remain at a height which continues 



