37-2 



MESSES. F. GOTCH AND V. HORSLEY 



Thus the degree of anaesthesia in which the animal happens to be influences the 

 result very considerably, and is a convincing proof of the true physiological basis of 

 the cord electrical effect, viz., that it is dependent upon the number and intensity of 

 excitatory impulses in the observed region. It may be pointed out once more that 

 this influence of anaesthesia is also sufficient to show, what might perhaps be otherwise 

 suspected, that there is no objection to the use of the electrical method of stimulation 

 through its possibly involving errors due to electrical escape. 



Further proof that with the method of isolation used no such escape occurs is 

 shown by the similarly directed effect evoked by both the make and break induction 

 shocks, and by the production of the effect by mechanical stimulation. A still more 

 convincing proof is, however, the complete disappearance of the effect on systemic 

 death. (See Chapter III., section 4.) 



B. Systemic death and injury. 



The influence of systemic death upon the physiological condition of the spinal cord 

 has been already referred to in connection with the resting difference. It was there 

 stated that the difference keeps up and increases in the exposed portion of cord as 

 long as it is in connection with a part which through the maintenance of an unim- 

 paired circulation retains its normal state of nutrition. When systemic death occurs 

 the difference immediately begins to fall, and in a very few minutes (2-5) the 

 excitatory electrical effect disappears, the loss of excitability occurring in the case of 

 the spinal cord with much greater rapidity than in the case of the sciatic nerve. 



This disappearance occurs without systemic death if by any movement of the animal 

 the cord is pulled upon, or if it is bruised in preparation at a point intervening between 

 the seat of excitation and that of observation. Finally, the functional endurance of 

 the tissue is dependent upon the animal used, differing in different species and in 

 the different animals of the same species. 



The most important general conditions by which the cord electrical effect is con- 

 trolled, having been thus set forth, we pass on to consider what information a detailed 

 examination of the characters and amounts of the electrical effects evoked under 

 different circumstances, furnishes as to the structure and functions of the spinal cord. 



