1012 



PHYSIOLOGY 



shaped depression, the other a conical depression for the points of a 

 small mirror holder, s. The third leg of the mirror holder rests 

 on the middle of the rubber membrane. The mirror itself is 1 cm. in 

 diameter. Any excursion of the membrane is thus transmitted to the 

 mirror, and the movements of the latter are recorded by reflecting a 

 beam of light from it through a slit 

 on to a photographic paper fixed on 

 a kymograph, which is situated in 

 a dark room or dark box. The 

 cannula is shown in Fig. 394. It is 

 composed entirely of metal, and is 

 fixed on to the cone-shaped ex- F IG . 394. 



tremity of the manometer, where it 



is held in place by the screws s. The vibration frequency of the moving 

 mass in this instrument is 180 per second, and it will indicate not only 

 the rapid changes of pressure occurring in the heart and blood-vessels 

 at each beat, but also the fine vibrations which are associated with 

 the heart sounds. The mass moved for a given change of pressure is 

 smaller than in any other instrument except the capillary mano- 

 meter, which was devised by Bayliss and the author for similar 

 purposes. 



By the introduction of a valve in the tube leading from the mano- 

 meter to the heart it may be used as a 

 maximum and minimum manometer 

 (Fig. 395). If the valve permits fluid to 

 go only towards the heart the mano- 

 meter will indicate the minimum pres- 

 sure attained during the cardiac cycle. 

 If it be turned the other way it will 

 indicate the maximum pressure. 



On registering the endocardiac 

 pressure by means of a manometer 

 capable of recording the quick changes 

 in pressure that occur in the ventricle 

 with each heart-beat, a curve is 

 obtained similar to that shown in 

 Fig. 396. Before we can interpret 

 this curve properly we must super- 

 pose on it another curve taken simul- 

 taneously and representing the altera- 

 tions of pressure occurring at the 

 beginning of the aorta. Only by the comparison of the two curves is it 

 possible to determine the exact points at which the aortic valves open 

 and close. The beginning of systole is marked often by a small rise in 



max. valve 



to manometer 



mm. valve 



to heart 



FIG. 395. V. FRANK'S valve. 



This is placed in the course of 

 the tube between heart and mano- 

 meter, so that the latter may be 

 used as a maximum, minimum, 

 or ordinary manometer, according 

 to the tap which is left open. 



