360 



THE CIRCULATION OF THE BLOOD. [CHAP. XXVIII. 



The instrument is now adapted by means of a pipe provided with 

 a stopcock (F) to the artery in which the blood is to be measured. 

 On opening the stopcock the blood rushes into the horizontal tube, 

 mingles with the alkaline solution, and pushes down the mercury, 

 in the vertical tube B', that in the tube B rising to the same extent 



Poiseuille's h&madynamometer as slightly modified by Volkmann : AA' the board to which 

 the bent glass tube (BB'B") is attached. CC'C" a tin tube which ia fixed through a cork (D) 

 air-tight to the horizontal branch of the glass tube. E an opening with a stopcock in this tube. 

 F a conical tube which may be introduced into an artery or vein. This is produced with a stop- 

 cock which serves to regulate the admission of the blood into the tube of the haemadynamometer. 

 GHG' an arm of wood connected with the board which serves to support the tin tube, and so 

 protect the horizontal branch of the glass tube. 



as the first is depressed. The rise and fall of the mercury in each 

 vertical branch can be measured on scales placed behind them, 

 and as the rise and fall are equal, the double of either will give 

 the height of a column of mercury which the force of the stream 

 of blood is able to maintain. By causing the blood to press upon 

 a column of mercury, Poiseuille got rid of the necessity of having 

 a very long tube as used by Hales. 



Hales inferred, from his observations on the lower animals, and 

 a comparison of the measurements of their arteries with those of 

 man, that the force of the heart in the human subject is capable 



