ON THE MAMMALIAN NERVOUS SYSTEM. 



401 



SECTION of both Posterior Columns. 



PREVIOUS Operation, Division of both Posterior Columns. 



The differences between the results obtained from sections made at the time and 

 beforehand, are perhaps those involved by the necessity in the latter case of using a 

 slightly stronger stimulus. And since the different column effects are similar in both 

 cases, the massed average of both lateral and both posterior effects evoked with the 

 minimal and maximal stimulus respectively may be taken from all three animals. 



Effect evoked by lateral columns. 



Minimal excitation, 55; maximal excitation, 136. 



Effect evoked by posterior columns. 



Minimal excitation, 4 ; maximal excitation, 46. 



It will be seen on looking at these averages, that with minimal excitation the 

 posterior column effect practically disappears as the consequence of the interruption 

 produced by the section ; thus the view as to the localisation of both stimulus and 

 generated impulse to these columns is true of afferent as of efferent impulses, when 

 the former is sufficiently weak. 



With a relatively more intense stimulus (or with the animal less etherised), this 

 localisation of the effect does not occur ; the excitation of the lower and posterior 

 columns now evokes effects above the interruption, the average Jimount of which is as 

 much as one-third that produced by the stimulation of the laterals, that is to say, 



* For full desci'iption of this animal as regards its condition during life and the post mortem, appear- 

 ances of the cord, see p. 439. 



MDCCCXCI. B. 3 F 



