THE VELOCITY OF THE WILL. 363 



scribed parallel to a part of the tracing by the muscle, to arrive direct- 

 ly at the time corresponding to the tracing. Marey detected, by this 

 method, degrees of speed in transmission varying from 30 to 61 feet. 



Moreover, the nerve-current travels more slowly at low tempera- 

 tures than at high ones. Dr. Munk discovered, besides, that the speed 

 is not alike in the different parts of a nerve ; in the motor nerves it 

 seems to increase toward the point of attachment of the muscle. And, 

 according to De Bezold, this speed decreases when the nerve is under 

 the influence of an electric current. 



The point was now to repeat these experiments on the human sub- 

 ject. It was found possible to conduct them in this manner : An elec- 

 tric current produces a slight sensation of pain on one point in the 

 skin ; the instant of action by the current is marked on the revolving 

 cylinder of a chronoscope. As soon as the person experimented on 

 feels the shock, he gives a signal by touching an electric key, and a 

 second mark is produced on the same cylinder. Measuring the inter- 

 val comprised between these two marks, we have the time that elapses 

 between the two signals. This time, which is from one to two-tenths 

 of a second, is made up of several parts; transmission of external im- 

 pression to the brain, perception, reflection, transmission of the will to 

 the fingers, muscular contraction, which is the result ; but, if the stim- 

 ulus is applied successively to different points on the skin, these delays 

 are always the same, except that which is due to the transmission of 

 sensations. If, for instance, a point on the great-toe is first excited, 

 and aftei*ward a point in the inguinal region, the difference in the .de- 

 lays remarked will represent the time employed by sensation in ascend- 

 ing from the foot to the middle of the body. 



These experiments were first made in 1861 by Hirsch, director of 

 the Neufchatel Observatory, by means of an apparatus which it would 

 take too long to describe here. The person experimented on touched 

 an electric key with the right hand at the instant of feeling that slight 

 pain, not unlike a pin-prick, which the knob of an induction apparatus 

 produces on touching the skin. The knob was applied in succession 

 to the cheek, then to the left hand, then last to the left foot. The 

 time lost in the transmission of this stimulus from the point touched 

 to the right hand was found equal, in the three cases respectively, to 

 T u_ ? ^-^ and T W of a second ; it required, therefore, yf^ of a second 

 for sensation to arrive from the left hand at the head, and -j-f^ for 

 its passage from the foot to the head. Hirsch inferred from tins 

 that the nerve-current travels over a distance of six feet and a frac- 

 tion i n T |L_ of a second, or about 104 feet in a second. Dr. Schelske 

 repeated these experiments in a more thorough way at the Utrecht 

 Observatory. He arrived at 91 feet as the speed of transmission of 

 sensation in the human body. The same experimenter proved that 

 the passage takes place with the same rapidity in the spinal marrow 

 as in the nerves. This result is the more remarkable, as the nerve- 



