262 



CIRCULATION. 



Fig. 6. 



ations, depending upon the condition of the heart and ves- 

 sels, the quantity of blood, respiration, muscular exercise, etc. 

 All experiments on the arterial pressure are made on the 

 principle of the experiment of Hales, which, with reference 

 simply to the constant pressure in the arteries, is as useful as 

 those of later date, and much more striking. The only in- 

 convenience is in the manipulation of the long tube, but this 

 may be avoided by setting it in a strip of wood, when it can 

 be easily handled. If a large artery, as the carotid, be ex- 

 posed in a living animal, and 

 a metallic point, connected with 

 a vertical tube of small caliber 

 and from seven to eight feet 

 long by a bit of elastic tubing, 

 be secured in the vessel, the 

 blood will rise to the height of 

 about six' feet, and remain at 

 this point almost stationary, 

 indicating by a slight pulsatile 

 .movement the action of the 

 heart. On carefully watching 

 the level in the tube, in addi- 

 tion to the rapid oscillation co- 

 incident with the pulse, another 

 oscillation will be observed, 

 which is less frequent, and 

 which corresponds with the 

 movements of respiration. The 

 pressure, as indicated by an 



Hemodynamometer of Poiseuille, modified elevation of the fluid, is sligllt- 

 by Ludwip, Spengler, and Valentin. The n 



instrument is connected with the vessel ly increased during CXpira- 

 V V, in such a manner that the circula- * ..TIT. 



tion is not interrupted. The elevation of tion, and diminished during 

 the mercury in the branch B C indicates ' 



the amount of pressure (BECLAKD, Phy- inspiration. 1 

 t^oloff^e, Paris, 1859, p. 204.) 



1 In all these experiments on the arterial or cardiac pressure, it is necessary 

 to fill part of the tube, or whatever apparatus we may use, with a solution of car- 

 bonate of soda, in order to prevent coagulation of the blood as it passes out of 

 the vessels. 



