viii CONDUCTIVITY AXD EXCITABILITY OF XERVE 71 



stimulus is strengthened, reflex movements occur in both legs, and 

 subsequently in the arms and trunk. This implies diffusion of 

 excitation over nearly the whole spinal cord, and almost all the 

 motor nerves which originate in this part of the central organ 

 are reflexly excited. The movements, however, are still co- 

 ordinated throughout, i.e. the groups of simultaneously excited 

 motor fibres are always in physiological correlation. 



The transmission of excitation to remote muscles must 

 obviously take a longer time under these conditions. If the 

 reflex period is estimated for a muscle of the same, and for one 

 of the opposite side (on stimulating a given point of the skin), the 

 reflex time of the latter exceeds that of the former. The amount 

 of this difference is the time of cross -conduction. There is 

 apparently less resistance in the longitudinal direction of the 

 spinal cord (Wundt, 29). 



The specific characteristics of conductivity within the central 

 nervous organs are least ambiguous in the striking changes 

 which result from the action of certain poisons. It has long 

 been known that in most vertebrates, after intoxication with 

 strychnin, the slightest stimulation of any sensitive part evokes 

 exaggerated uncoordinated muscular movements (spasms), which 

 in warm-blooded animals soon end in death. Both earlier and 

 later experiments concur to show that the spinal cord is an indis- 

 pensable factor in strychnin-spasm, as in the initiation of reflex 

 movements. Neither in peripheral motor nor in sensory nerves is 

 excitability perceptibly modified by the poison. Strychnin must, 

 therefore, be reckoned as a specific poison of the spinal medulla. 



The introduction of minute doses (0'02 0'04 ingr.) at first 

 produces no change in the frog, beyond a marked increase of 

 reflex excitability. The reflex twitches appear with weaker 

 stimuli, and with greater precision at each successive stimulus ; 

 neither in the duration of the latent period nor in the subse- 

 quent course of the twitch is there any perceptible divergence 

 from ordinary reflex twitches. After somewhat larger doses 

 (while, according to Eosenthal, the length of the latent period 

 steadily decreases Wundt states the contrary) the twitch changes 

 gradually into a sustained tetanus, which appears with even the 

 weakest stimuli, and is little increased with stronger excitation. 

 At the climax of the strychnin effect, any stimulus capable of 

 discharging the reflex at once produces maximal excitation. As 



