CHAP, iv.] THE VASCULAR MECHANISM. 195 



This consists essentially of a very small metal drum or tambour 

 (Fig. 41 a) somewhat like that of Mare}^ but 

 hemispherical and not more than 15 mm. in 

 diameter, ending below in a tube b. In Fig. 

 40 the instrument, with its holder, is seen from 

 above. The second lever, which is motionless, 

 is for the purpose of describing the base line. 

 The screw-tap on the tube leading, in the figure, 

 up to the tambour, is for the purpose of diminish- 

 ing the calibre of the tube and so of 'damping ' 

 the instrument. On the right of the tambour in 

 the figure are seen the arrangements for adjust- 

 ing the levers. In Fig. 41 the tube b by which 

 the catheter is connected with the tambour, 

 is, for convenience of illustration, shewn as FlG - 41 - 

 directed parallel to the lever, instead of, as 

 in the instrument itself, at right angles to it. THLE'S MEMBRANE MA- 

 The roof of the tambour is supplied by a care- NOMETER. 

 fully chosen delicate elastic membrane c which 



bears at its centre a thin metal disc d, connected by a short upright 

 e with a lever I. 



A catheter, opened at the end or with a lateral 'eye ' and filled with 

 a solution of magnesium sulphate or with some fluid tending to check 

 the clotting of blood, is introduced into the cavity of the heart which 

 it is desired to explore. It may be introduced by the jugular vein into 

 the right auricle, and past the auricle into the right ventricle, or through 

 the carotid artery into the aorta, and so, between the semilunar valves, 

 or piercing one of the flaps (the perforation seems to introduce no error) 

 into the cavity of the left ventricle ; or the end of the catheter may be 

 left in the aorta above the semilunar valves when it is desired to 

 Investigate the pressure at the root of the aorta. The cavity of the 

 tambour also is filled, not witli air, as in Marey's tambour, but with the 

 same fluid as is the catheter, or with water j and the tube of the tambour 

 is connected with the catheter. 



Variations of pressure within the cavity of the heart are transmitted 

 through the fluid of the catheter to the fluid in the tambour, and thus put 

 into movement the elastic roof of the tambour ; the movements of the 

 elastic roof are, in turn, transmitted to the lever, which records, in the 

 usual manner, on some recording surface. For measuring the amount 

 of the changes of pressure, the instrument must be graduated expert 

 mentally. There are many details in the instrument which need not be 

 described here ; but we may state that the instrument may be ' damped,' 

 rendered less sensitive, and thus the features of the curves due to 

 inertia lessened, by narrowing, through a screw-tap, the communication 

 between the catheter and the cavity of the tambour. 



The membrane of the tambour may, by means of an ivory button, 

 be brought to bear on one end of a slip of steel, placed horizontally 

 and fastened at the other end, so as to act as a spring. The instrument 

 then becomes a " spring-manometer." The small movements of the 

 spring caused by the movements of the membrane of the tambour are 

 magnified by a recording lever. 



