190 



THE CIRCULATION OF THE BLOOD 



phate, to fill the apparatus from a bottle suspended at a height about that 

 of the pressure to be measured, and capable of being raised or lowered as 

 required for the purpose. The cannula inserted and tied into the artery 

 may be of several different kinds. A glass T-tube with the end drawn out 



FIG. 185. Arterial Cannula. T-form for convenience in washing out clots. 



and cut so that it is oblique, and provided with a slightly constricted neck 

 to prevent its coming out of the artery easily, is a very convenient form, 

 figure 185. Of the two free ends of the T-cannula one is connected with the 

 manometer, the other with the pressure bottle. The peripheral end of the 



to 



*-*-* 



FIG. 186. Tracing of Normal Arterial Pressure in the Dog, Obtained with the Mercurial Man- 

 ometer. The smaller undulations correspond with the heart-beats; the larger curves with the re- 

 spiratory movements. Pressure is in millimeters of mercury as shown by the scale to the left. 

 Time in seconds. (New figure by March and Nugent.) 



cut artery is tied to obviate the escape of blood. By this means, the pressure 

 communicated to the column of mercury is the forward, and not the lateral, 

 pressure of blood, but there is very little difference. 



As soon as the experiment is begun, the writing float is seen to oscillate 



