THE GRAPHIC METHOD 



ogy, it is necessary to describe it here somewhat fully. The apparatus em- 

 ployed for recording movements by the graphic method consists essentially 

 of two parts: (a) the surface upon 

 which the movement is traced, and 

 (b) the mechanism by which the 

 movement is transferred to the re- 

 cording surface. 



A. THE KYMOGRAPH 



[A very simple illustration of the 

 graphic method is given in Fig. 1, where 

 the simple contraction of a frog's mus- 

 cle is being recorded on a moving sur- 

 face an application of the method first 

 made by Helmholtz in 1852. In such 

 an apparatus 1 the surface consists of a 

 glazed paper covered evenly with the 

 soot from a gas-flame and attached to 

 the surface of the drum (D) of an in- 

 strument called the kymograph. The 

 drum is caused to revolve in the direc- 

 tion of the arrow by a clockwork (CW) 

 inclosed in the base of the kymograph. 

 The clockwork is propelled by a strong 

 spring which is wound by means of the 

 lever at the left. By means of the 

 thumbscrews (AS) and fans (F) of 

 different sizes, the gearing of the clock- 

 work may be so adjusted as to revolve 

 the drum at any desired speed. 



The recording lever (RL) termi- 

 nates in a fine point which bears 011 the 

 smoked surface, and, as the drum re- 

 volves, scratches a tracing in the soot. 

 The muscle, the gastrocnemius of a frog*, 

 is so prepared that its tendon of Achilles 

 is free to be attached to the hook on 

 the lever. The other end of the muscle is 

 still attached to the femur, a stump of 

 which is left to be fastened in the clamp. 

 In order to imitate as nearly as pos- 

 sible the action of the muscle in its 

 normal relations, it is necessary that 

 it be made to lift some weight (W) 



i. e., to do a certain amount of work. This weight, however, has considerable 

 inertia compared with the lever itself, and in order that this may influence the 

 character of the contraction as little as possible, the weight is fastened to the lever 

 quite close to its axis, the muscle itself being fastened somewhat farther from the 

 axis. Electrical connections are made so as to send a shock through the muscle. 



FIG. 2. Muscle curves recorded one above 

 the other on the same drum ; to be read 

 from right to left. The vertical line marks 

 the moment of stimulation. 



1 For the sake of simplicity the recording surface in the figure is shown white, and the 

 tracing black. 



