PHYSIOLOGIC APPARATUS. 



683 



THE GRAPHIC METHOD. 



The term graphic is applied to a method by which curves or tracings 

 are obtained which represent the extent, duration, and time relations of 

 the movements accompanying physiologic processes. If these movements 

 can be translated in one direction, they may be recorded in different ways: 



1. By attaching the moving structure e. g., heart, muscle, etc. to a 



delicate lever the free extremity of which is provided with a writing 

 point. 



2. By transmitting the movement through a column of air enclosed in a 



rubber tube the two ends of which are attached to a metallic capsule, 

 covered by a 

 rubber mem- 

 brane, termed 

 a drum or tam- 

 bour. When 

 the membrane 

 of the first tam- 

 bour is pressed 

 or driven in- 

 ward, the air is 

 forced through 

 the rubber tube 

 into the second 

 tambour and its 

 membrane is 

 pushed out- 

 ward. As soon 



as the primary pressure is removed, the membranes return to their 

 former condition. If the membrane of the first tambour is drawn 

 outward, the air in the system is rarefied and the membrane of the 

 second tambour is pressed inward. For the purpose of register- 

 ing the movement 

 transmitted by the 

 column of air, the 

 second tambour is 

 provided with a 

 light lever support- 

 ed by a vertical 

 bearing resting on 

 a small metallic 

 disk. The mem- 

 brane of the first 



tambour is frequently provided with a button, which is placed over 

 the moving structure. The inward movement of the membrane of 

 the first tambour produces an outward movement of the membrane of 

 the second tambour, indicated, though magnified, by the rise of the 

 free end of the lever. The reverse movement of the membrane is 

 attended by a fall of the lever. The first tambour is termed the 

 receiving, the second the recording tambour (Figs. 344, 345). 



FIG. 344. A RECEIVING TAMBOUR. 



FIG. 345. A RECORDING TAMBOUR. (Marey.} 



