Chap. xvii.] MAKERS MYOGRAPHION. 177 



in the forceps and attached to the lever, the marker of 

 which is against the glass plate, a curve of muscular 

 contraction is obtained. A mark can be made in the 

 plate indicating the moment the contact is broken, and 

 it can be seen whether the moment of contraction 

 coincides with this. The latent period of stimulation 

 can thus be measured, and if the stimulation be made 

 by the nerve, and the experiment be repeated by 

 stimulation at two different points of the nerve at some 

 distance from one another, as described on page 1 82, 

 the rapidity of the nerve current can also be estimated. 

 The newest addition to the spring myographion con- 

 sists in the adaptation of a tuning fork whose stylet 

 projects on the lower part of the plate. An ingenious 

 contrivance liberates the plate and at the same time 

 causes the fork to vibrate, so that curves of the oij-oth 

 of a second or so, according to the fork, are obtained 

 simultaneouslv with the contraction, to facilitate the 



V ' 



estimation of time. 



An arrangement adopted by Marey and shown in 

 Fig. 88 is specially advantageous, because the muscle 

 and nerve experimented on are not removed from the 

 frog but left in situ, so that drying is prevented and 

 nutrition is carried on. A frog is pithed and pinned 

 down on a frog-plate of cork, which is supported on 

 a brass upright. A slit in the skin of one leg over 

 the tendo Achilles is made, and the tendon freed from 

 its insertion. At the end of the frog-plate is a stylet, 

 attached to a spring, which is made to project on to 

 the surface of a cylinder, as seen in the figure. A 

 piece of thread tied to the tendon is attached to a 

 small hook at the side of the lever. If the muscle 

 contracts, the lever is pulled to one side ; when the 

 muscle relaxes, the elasticity of the spring returns the 

 lever to its original position. If the point of the 

 lever is resting on the surface of the revolving 

 cylinder, a curve of muscular contraction will be 



M 7 



