Chap, iv.] THE VASCULAR MECHANISM. 



199 



employed as the plethysmography chamber, the changes of- volume in 

 it being transmitted by air to the recording apparatus. A cannula is 

 introduced into the pericardium, a little air entering at the same time, 

 and is connected by an air tube with a delicate piston, the movements 

 of which are recorded in the usual way. 



f •* ^ "pi — "- 



Fig. 44. Cardiometer of Roy and Adami. 



In the method of Roy and Adami the heart is placed in a rigid 

 metal box, Fig. 44 b, the cavity of which, filled with warmed oil, is 

 connected with a light piston c and so with a recording lever. The 

 pericardium being laid open, the two halves of the box are placed 

 round the heart, are securely fixed by means of an india rubber ring a, 

 to the parietal pericardium round the roots of the great vessels, and are 

 brought together. The cavity 

 also filled with oil, is 



brought 



is then filled with oil, and the piston, 

 into connection with the box, the lever 



