370 THE NEKVOUS SYSTEM. 



the finger is the same in all cases, the difference between successive 

 observations is due to the different lengths of nerve transmitting the 

 impression. 



In the experiments of Burckhardt, made on thirteen different per- 

 sons, the mean rate of transmission for sensitive impressions through 

 the nerves was a little less than 41 metres per second ; that is, more 

 than one and a half times as rapid as that for voluntary motion. 

 The variations were from a minimum of 20 to a maximum of 73 

 metres ; but in nearly three-fourths of all the observations, the results 

 were confined within the limits of 40 and 56 metres. The rapidity 

 of transmission varied but little with the intensity of the impres- 

 sion ; the difference, on the average, being but little over one per 

 cent. The average rate for different kinds of nervous action is 

 accordingly as follows : 



RATE OF TRANSMISSION THROUGH THE SERVES. 

 For voluntary motion . . . .27 metres per second. 

 For sensation 47 " " " 



Rate of Transmission in the Spinal Cord. The investigations of 

 Burckhardt first indicated a difference between the rate of transmission 

 in the spinal cord and that in the nerves. This rate was determined 

 for the spinal cord by comparing the passage of a voluntary impulse 

 through two nerves, like the sciatic and the ulnar, which emerge 

 from the spinal cord at different points. In this case the impulse, after 

 leaving the brain, traverses different lengths of the spinal cord ; and as 

 its rate of movement in the peripheral nerves is known, the difference 

 in time of its entire passage gives its rate of movement in the spinal 

 cord. Thus a motor impulse, which calls into action the interosseous 

 muscles of the hand, passes through the cervical portion of the spinal 

 cord, the lower cervical nerves, the brachial plexus, and the ulnar 

 nerve. An impulse which excites contraction in the quadriceps exten- 

 sor cruris passes through the cervical and dorsal portions of the 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 case as in the first ; and the amount 

 of its retardation must correspond with .this difference. 



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 rapid- 

 ity of transmission through the nerves and the spinal cord is very 

 manifest. 



A comparison of the opposite sides of the body gave a difference 

 in the rate of transmission, for the right and left halves of the spinal 

 cord, of from one to three metres per second, always in favor of the 

 left side. 



The transmission of sensitive impressions through the spinal cord, 



