430 NERVOUS IRRITABILITY 



the spinal cord, and thence through the lumbar plexus and the anterior 

 crural nerve to the thigh. Consequently its transit through the spinal 

 cord is about three times as long in the second instance as in the tirst ; 

 and its amount of retardation will indicate the rate of transmission in 

 the spinal cord as compared with that in the nerves. 



By this means it was found that the transmission of voluntary motor 

 impulses in the spinal cord is considerably slower than in the nerves. 

 Its average rapidity was a little over 10 metres per second ; the mini- 

 mum being 8, the maximum 14 metres. Thus the difference in rapidity 

 of transmission through the nerves and the spinal cord becomes very 

 manifest. 



TRANSMISSION OF VOLUNTARY MOTOR IMPULSES. 

 Through the spinal cord . . . .10 metres per second. 

 " " nerves . . . . 27 " 



A comparison of observations on the two opposite sides of the body 

 gave a difference in the rate of transmission, for the right and left 

 lateral halves of the spinal cord, of from 1 to 3 metres per second, 

 always in favor of the left side. 



The transmission of sensitive impressions through the spinal cord, 

 on the other hand, was found to be nearly as rapid as through the 

 nerves, the average rate being a little over 42 metres per second. A 

 remarkable difference, however, appeared in the transmission of simple 

 tactile impressions and of those which were painful in character. The 

 former are comparatively rapid, as above stated, while painful impres- 

 sions are communicated through the spinal cord at a much slower rate, 

 amounting on the average to not more than 13 metres per second. 

 Thus the transmission of motor impulses and of tactile and painful 

 impressions respectively, through the spinal cord, is as follows : 



RATE OF TRANSMISSION THROUGH THE SPINAL CORD. 

 For tactile impressions . . . .42 metres per second. 



" painful 13 " 



" motor impulses ... . 10 " 



According to these results the passage of a motor impulse, from the 

 brain to the muscles of the foot, would occupy 0.088 of a second ; of 

 which time about one-half would be required for transmission through 

 the spinal cord, and one-half for transmission through the fibres of the 

 sciatic nerve. 



Rapidity of Nervous Action in the Brain. In all the experiments 

 detailed above, an essential part of the nervous operation consists in 

 the hearing of the signal for a voluntary movement and in the act of 

 volition which sets in motion the voluntary impulse. This process, 

 which takes place in the brain, includes both the action of the gray 

 substance of the nervous centres and its transmission b} r the nerve 

 fibres of the white substance to the origin of the spinal cord. The time 

 thus consumed is ascertained by deducting, from the whole period 

 intervening between the signal given and the contraction of the muscle, 



