196 



P:SSENTIALS OF PHYSIOLOGY. 



raising the membrane of the manometer and the lever : the movements 

 of the lever are recorded graphically on a kymograph. 



FIG. 66. Marey's tambour. The writing point of the lever is not 

 shown. (From Messrs Baird & Tatlock.) 



The method is unsatisfactory, because, in the first place, it is only 

 applicable to large animals, and, secondly, because, owing to the com- 

 pressibility of the air contained in the apparatus arid to the oscillations 

 of the membrane of the manometer, waves are produced upon the 

 tracing which sometimes render it inaccurate. 



These drawbacks are considerably diminished in Hiirthle's method, 

 the essential features of which are (1) the use of a very small manometer 

 withfa thick rubber membrane (fig. 67), (2) the substitution for the 



sound of a tube opening directly 

 into the ventricle, and (3) the 

 filling of the whole apparatus, 

 including the tambour, with fluid 

 (half-saturated sodium sulphate 

 solution). 



A still better manometer has 

 recently been devised by Piper, 



in which instrumental errors are almost completely excluded (fig. 68). 

 It consists of a metal cannula A, 6 cm. in length, containing a trocar 

 B, by the aid of which the cannula can be thrust through the wall of 

 the auricle or ventricle into the cavity of the heart. It is filled with 

 saline solution containing hirudin, and even the smallest air bubble must 

 be excluded. The cannula expands at C to form a small chamber, one 

 wall of which is covered by a thick stretched rubber membrane D ; to 

 the outer surface of this membrane a tiny plane mirror E is attached. 



When the cannula has been pushed into the heart and tied in 

 position, the trocar is withdrawn and the tap F is closed so as to 

 prevent the escape of blood ; the cannula is then fixed with a clamp. 

 As the endocardiac pressure varies, the membrane bulges or shrinks 

 slightly and the position of the mirror alters ; these movements are 

 recorded and greatly magnified by throwing on to the mirror a beam 

 of light, which is reflected on to a kymograph covered with photographic 

 paper and excluded from other sources of light. 



FIG. 67. Hiirthle's manometer. 



