550 CIRCULATION OF BLOOD AND LYMPH. 



long diameter. The apex beat is proof that the apex remains 

 against the chest wall during systole and in mammals corroborative 

 experiments have been made by running needles through the chest 

 wall into the base and the apex of the heart. Such needles act as 

 levers with a fulcrum in the skin, and from the movement of the 

 projecting portion it has been shown that, while the basal portion 

 of the heart moves downward during systole, the apex remains 

 more or less stationary except for the lateral movements due to 

 the rotation. 



The Cardiogram. The apex MCCA,O may be recorded easily by 

 means of appropriate tambours. Several instruments have been 

 especially devised for this purpose and are designated as cardio- 

 graphs. The cardiograph described by Marey is shown in Fig. 228. 

 It consists essentially of a tambour inclosed in a metal box. The 



229. Two cardiograms from the same individual to show characteristic records: a. 

 Beginning of systole ; b-c, systolic plateau. (After Marey.) 



rubber membrane of the tambour carries a button which can be 

 brought to bear, under a suitable pressure, upon the apex of the 

 heart. The movements of this button cause pressure changes in 

 the air of the tambour which are transmitted through tubing to a 

 recording tambour and recorded on a kymographion. A simple 

 and effective cardiograph may be made by pressing a funnel 

 against the skin over the apex and connecting the stem of the 

 funnel by tubing to a suitable recording tambour. The car- 

 diograms obtained by such methods have been the subject of 

 much discussion. The form of the curve varies somewhat with 

 the instrument used, the way in which it is applied, the position of 

 the heart apex with reference to the chest wall, and with the con- 

 ditions of the circulation, and it is often difficult to give it a correct 

 interpretation. An uncomplicated form of the cardiogram is 

 represented in Fig. 229, 7, and a curve more difficult to interpret in 

 Fig. 229, 8. Owing to the number of factors that alter the char- 

 acter of these curves they have not proved to be very useful in the 

 accurate study of the character and time relations of the heart beat. 



