332 MESSRS. F. GOTCH AND V. HORSLEY 



(e.) Electrical Change in Cord produced by &quot; Semi-voluntary&quot; Cortical Discharges. 



During prolonged etherisation it is well known that animals of all kinds, including 

 Human beings, occasionally make unconscious, but semi-voluntary, purposive move 

 ments. These movements are abolished by very profound anaesthesia. 



Electrical effects manifest themselves in the observed portion of exposed spinal 

 cord when these semi- voluntary movements occur in the upper limb and trunk muscles. 

 The effects are evidenced in the galvanometer connected with the tissue by deflec 

 tions, which, though resembling the excitatory variations in being always opposed in 

 sign to that of the resting difference, vary very much in amount and rapidity of 

 development. It is obvious that the excitability of the cortex and the intensity of 

 the exciting agency, must be the chief agents in determining the amount of this 

 effect. The extent of such a deflection when, as evidenced by well-marked move 

 ments of the muscles on both sides in the upper half of the body, a considerable 

 cortical discharge of energy was taking place, has amounted in the Monkey to 360 

 scale ; it was however, at once abolished by profound ansesthetisation. As a rule the 

 deflections amounted to from 20 to 60 scale ; no doubt they would have been larger, 

 had it not been for the fact that, since their appearance interfered with accurate 

 observation of cortical effects evoked by stimulation, we always took care on perceiving 

 them to so alter our conditions of anaesthesia as to abolish this source of error. 



2. Electrical Changes in the Sciatic Nerve. 



After having thus considered the electrical changes produced in the spinal cord by 

 the functional activity of the cortex, we next turned our attention to the more 

 complex question of what occurs in the peripheral nerves when the cortex is excited. 

 This is obviously more complex, because, although we are still exciting the cortex, we 

 have now introduced into the mechanism the bulbo-spinal system of centres, so that 

 we are brought at once face to face with the question as to how far the changes which 

 we have just been studying in the spinal cord are modified by the as yet hypothetical 

 termination of the fibres of the pyramidal tract in the said bulbo-spinal centres. 



We are justified in expressing this query in a still simpler fashion : what becomes 

 of the cortical impulses when they reach the bulbo-spinal centres ? Other things 

 being equal, it might have been expected that we should have got very clear evidence 

 of the effect of active excitatory change in the peripheral nerve, seeing that if this 

 had been still in connection with the muscle, the muscle would have been thrown into 

 a powerful series of contractions. It was, therefore, with very considerable surprise 

 that we observed what a relatively small electrical variation was obtainable in the 

 sciatic nerve when the corresponding portion of the cortex was excited. The experi 

 mental procedure was extremely simple, and as follows : The cortex was exposed, as 

 described, and the sciatic nerve on the opposite side of the body was also exposed, 



