368 THE NERVOUS SYSTEM. 



which pushes aside the lever, causing in the traced line a momentary 

 deviation (d), which thus registers the instant of the stimulation of 

 the nerve. The muscle used for experiment is attached by its tendon 



FIG. 96. 



DIAGRAM OF THE REGISTERING APPARATUS, according to the plan of Marey. a. Undulating line 

 traced by the tuning-fork, which marks the time consumed by the card in moving from one point to 

 another. 6. Line traced by the first lever, forming part of tin- galvanic circuit, c. Line traced by 

 the second lever, which is moved by the contraction of the muscle, d. Deviation of the line 6, 

 indicating the closure of the galvanic circuit and the stimulation of the nerve, e. Deviation of 

 the line c, indicating the muscular contraction. 



to a second lever in such a way that any muscular contraction will 

 draw aside its free extremity. This lever, while at rest, traces a second 

 horizontal line (c) below the first ; and when the muscle contracts, the 

 line is deviated, as at (e), by the movement of the lever. 



There are thus left upon the registering surface two deviations, d and 

 e, one of which records the stimulation of the nerve, the other the 

 muscular contraction ; and between the two there is a certain interval. 

 The number of undulations in the trace a, corresponding to this interval, 

 indicates the time which has elapsed between the stimulation of the 

 nerve and the muscular contraction. In the example shown at Fig. 96, 

 as the interval between the deviations includes 13 simple vibrations, of 

 which 500 would represent one second, the time occupied is 0.026 of a 

 second. By this means, intervals of very short duration may be accu- 

 rately registered. 



Subsequently investigations of a similar kind w^ere applied to the 

 man during life. In the experiments of Baxt,* this was done by 

 applying electrodes to the skin over the median nerve, at varying 

 distances from its muscular distribution. The nerve was thus stimu- 

 lated at the wrist, at the elbow, and at the upper arm ; the effect being 

 marked by the swelling of the muscles at the ball of the thumb. The 

 time intervening between the application of the electrodes and the 

 muscular contraction was greater with the stimulus applied at the upper 

 arm, than at the wrist ; the difference being evidently the time required 

 to transmit of the nervous impulse from the first point to the second. 

 The rate of transmission, as ascertained by these experiments, varied 

 according to the conditions of cold or warmth ; being less rapid at a 

 low than at a high temperature. 



* Monatsbericht der koniglichen Prenssischen Akademie, 1867 and 1870. 



