STIMULI AND THEIR ACTIONS 



361 



a second ; in the lobster, as Leon Fredericq and Van de Velde 

 have shown, it is less and amounts to about 6 m. in a second. 

 Various methods have been devised for determining the rate 

 of transmission in the nerve, an undertaking that with the great 

 rapidity of the process is not easy. The principle of all these 

 methods depends upon the determination of the difference in time 

 between the appearance of a muscle-contraction, when the nerve 

 belonging to it is stimulated very near the muscle, and its 

 appearance upon stimulation of the nerve at a more remote place 

 (Fig. 153). For this purpose the spring-myograph of du Bois- 

 Reymond can be employed, an apparatus that serves for the 

 graphic representation of a muscular movement (Fig. 154). The 

 apparatus consists of a muscle-holder in which the gastrocnemius 

 muscle of a frog, the nerve of which 

 is freed, is fastened by the femur ; 

 the muscle is connected with a lever, 

 which accompanies every contraction 

 and by means of a fine point records 

 it upon a smoked glass plate which 

 is shoved rapidly by. The glass 

 plate moves in a sledge-like frame 

 in a vertical plane in front of the 

 writing-lever, and is put in motion 

 by a spring. Simultaneously with 

 the release of the spring an electrical 

 stimulus is let loose upon the nerve ; 

 moreover, a tuning fork is made to 

 vibrate, and traces its vibrations, 

 likewise by means of a writing-point, 

 upon the blackened glass plate. If 

 the nerve be stimulated once at a 

 distance of about 3 cm. from the 

 muscle, and once immediately at the 

 muscle, the first contraction follows 

 a short time later than the second, 

 because the first stimulus has a longer stretch than the second 

 to pass over before it can act upon the muscle. This difference 

 in time that in both cases elapses between the moment of 

 stimulation and the appearance of the contraction, can be 

 measured with extreme exactness upon the blackened plate, upon 

 which the contraction is traced in the form of a curve, by the 

 number of vibrations of the tuning fork that are traced simul- 

 taneously (Fig. 155). Since the number of vibrations of the 

 tuning fork in one second is known, the duration of a single 

 vibration can easily be computed, and from the number of 

 vibrations that lie between the beginning of the second contraction 

 and that of the first, the time can be calculated that elapsed 



FIG. 153. Gastrocnemius muscle of a frog 

 with the sciatic nerve. ^The femur 

 to which the muscle is attached, is 

 clamped in a muscle-holder, and the 

 nerve is stimulated first at 1, then 



ate. 



