HELMHOLTZ IN KONIGSBERG 



Suppose the difference of time between the registra- 

 tion of stimulating at the toe and at the thigh to 

 be y, then in the second experiment x = a-y + b + c; 

 that is, y = the time occupied by the passage of the 

 nerve current from the toe to the thigh. By this 

 method the velocity of the nervous impulse in the 

 sensory nerves in man is found to vary from 50 to 100 

 metres per second (160 to 30.0 feet). 



It will be noted that for motor nerves the obser- 

 vations were made on the frog and for sensory nerves 

 on man. The next question Helmholtz solved was : 

 Is the velocity the same or different in the two kinds 

 of nerves ? By attaching the thumb to a myograph 

 and then stimulating near the wrist and at the elbow, 

 it was found that the muscles of the thumb contracted 

 a little later after stimulation at the elbow ; that is to 

 say, the nervous impulse took some time in travelling 

 from the elbow to the wrist. Two curves were 

 obtained practically by the same method as was used 

 in determining the rate in the motor nerve in the 

 frog, and the velocity was found to be the same as 

 in the sensory nerves of man. In both kinds of 

 nerves, cold was found to retard and heat to acceler- 

 ate the velocity of transmission. 



These important observations not only threw light 

 on the question of the transmission of the nervous 

 impulse, but they prepared the way for the determina- 

 tion of time relations in many nervous processes. 

 Astronomers had long known that in watching and 

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