1888.] The Spinal Cord and the Cortex Cerebri. 19 



terminations of the efferent nerves. Now since the excitatory pro- 

 cesses originating in the cortex are conducted by the efferent channels 

 in the spinal cord, presumably the pyramidal tracts, the problem of 

 their relationship to the centres of the bulbo-spinal system cannot be 

 determined by experiments which record the mechanical changes in 

 the muscles. In order to ascertain what share respectively the centres 

 in the cortex and those in the spinal cord have in the production of 

 the characteristic epileptic sequence, the action of the latter must be 

 eliminated. This can be done by investigating the nature of the 

 excitatory processes in the cord when the efferent channels in the 

 dorsal region for the lower limbs are made the subject for observa- 

 tion. 



For this purpose we determined to obtain, if possible, evidence as 

 to the nature of the excitatory processes of the epileptic convulsion in 

 the spinal cord, as shown by "tapping" the cord and noting the 

 electromotive changes which, as is well known, accompany functional 

 activity in nerves. The results we have already obtained are so 

 harmonious and demonstrative, that we venture to make this prelimi- 

 nary communication, reserving full details for a subsequent account. 



PAET I. The Electromotive Change following a Single Excitation of the 

 Mammalian Nerve. 



Our first experiments were made for the purpose of ascertaining to 

 what extent we could detect an electromotive change following a single 

 excitation of a mammalian nerve. Since the discovery by du Bois- 

 Reymond of the fact that the excitatory process in nerve is accom- 

 panied by an electromotive change, the characters and time relations 

 of this change have been investigated by various observers, notably 

 by Bernstein, Hermann, Hering, and Head. The general result of 

 their observations is to show that the change following a single stimu- 

 lus is of very short duration, so short that the galvanometer gives 

 little evidence of its presence, and the observers referred to were 

 compelled to adopt the device first employed by Bernstein, which 

 involves repeated excitation and consequent summation of effect, a 

 method well known to physiologists as that of the repeating differ- 

 ential rheotome. For our purpose it was essential to obtain evidence 

 of the effect following one stimulus only, and this we were fortunately 

 able to do by using a sensitive Lippmann's capillary electrometer of 

 quick reaction, made by Mr. G. F. Burch, and belonging to Dr. Burdon 

 Sanderson, who kindly placed it at our disposal. This instrument, 

 when the capillary was magnified 400 times by the observing micro- 

 scope, gave a perceptible response when connected through a resistance 

 of 10,000 ohms for one-thousandth of a second with an electromotive 

 difference of only 0'003 D. The amount of movement of the mer- 

 cury was estimated by the divisions of a micrometer eyepiece, one 



C 2 



