480 



OF THE CIRCULATION OF THE BLOOD. 



or veins, however different in caliber. The tube is attached to a board (AA'), 

 on which a scale is marked. To use it, mercury is poured into the perpen- 

 dicular 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 experiment (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. 



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 stop- 

 cock the blood rushes into the horizontal tube, mingles with the alkaline solu- 

 tion, and pushes down the mercury, in the vertical tube B', that in the tube B 



Fig. 140. 



Poisseuille's Hsemadynamometer, as slightly modified by Volkmann : AA', the board to which the bent 

 glass tube (BB'B") is attached. C'C", a tin tube which is 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 intro- 

 duced into an artery or vein. This is provided with a stopcock, 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. 



rising to the same extent 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 main- 

 tain. By causing the blood to press upon a column of mercury, Poisseuille 

 got rid of the necessity of having a very long tube, as used by Hales. ED.] 



