160 



THE CIRCULATION OF THE BLOOD 



attachment of the semilunar valves. After being carried upward about 

 half an inch the needles were brought out again through the coats of the 

 respective vessels, so that in each vessel one valve was held back against 

 the arterial walls. Upon applying the stethoscope to the vessels it was found 

 that after such an operation the second sound had ceased to be audible. 



Tube to communicate 

 with the tambour 



\ 



Ivory Tape to attach 

 knob instrument to the chest 



Tympanum 

 FIG. iS5- Cardiograph. (Sanderson's.) 



Disease of these valves, when sufficient to interfere with their efficient action, 

 also demonstrates the same fact by modifying the second sound or destroying 

 its distinctness. 



The Cardiac Impulse. The heart may be felt to beat with a slight 

 shock or impulse against the walls of tlie chest at the level of the fifth inter- 

 Screw to adjust the lever 



i 



Writing lever 



Tambour 



Tube to the cardiograph 



FIG. 156. Marey's Tambour, to which the Movement of the Column of Air in the Cardiograph 

 is Conducted by a Tube, and from which it is Communicated by the Lever to a Revolving Cylinder 

 so that the tracing of the movement of the cardiac impulse is obtained. 



costal space on the left side. Its extent and character vary in different 

 individuals, a factor of considerable clinical significance, and therefore es- 

 pecially discussed in works on clinical diagnosis. The cause of the cardiac 

 impulse has been variously described. It will be remembered that during 



