170 STUDIES IN ADVANCED PHYSIOLOGY. 



and the slightest variations in pressure cause the rubber, 

 and consequently the recording lever resting on it, to move 

 up or down as the pressure is positive or negative. The 

 recording lever is then made to write on a suitable surface 

 which is moved along it. Rough cardiograms may be made 

 by connecting two tambour boxes with a rather inelastic 

 tubing, then firmly pressing one over the point in the chest 

 where the cardiac impulse is most perceptible, and arrang- 

 ing the other tambour for the usual way of recording. The 

 pulsations of the chest wall caused by the heart beat will 

 be transmitted through the system of tambours and be re- 

 corded on the moving surface. It may not be out of place 

 in this connection to call attention to the fact that this car- 

 diac impulse is not caused by the chest wall being tapped 

 or struck by the heart. The heart never leaves the chest 

 wall, but the impulse is caused by the sudden tension pro- 

 duced at this point when the systole occurs. Much as a 

 person might produce an impulse on a sensitive surface by 

 first laying his hand gently on the surface and then sud- 

 denly pulling it up into a fist without removing it from the 

 surface. 



On account of the thick wall which separates the tam- 

 bour from the heart these cardiograms do not give the finer 



Fig. 84. THE POINTS IN THE CARDIOGRAM OF THE VENTRICLE AT WHICH DIFFERENT 



PHYSIOLOGISTS PLACE THE OCCURRENCE OF THE SECOND SOUND. 



detail and are not altogether trustworthy. In their finer 

 determination there are still a number of points not yet per- 

 fectly established. Thus, observers have not been able to 



