516 MESSRS. F. GOTCH AND V. HORSLEY 



We have found, further, that the difference is subject to variations of which 

 the following are the most important : 



(a.) A notable fall is observed in all three tissues in consequence of systemic 

 death. 



(b.) The difference in the cord is increased after the functional activity of the organ 

 has been aroused. 



(c.) The difference in the cord is more pronounced when the tissue is in connection 

 with the encephalon. (See Chapter IV.) 



(2.) Effect in the Spinal Cord on Excitation of the Cortex Cerebri. 



In extension of our discovery that excitatory electrical effects can be observed in the 

 spinal cord to result from excitation of the cortex cerebri, as previously described, and by 

 means of which the character of the impulses derived from the cortical centres may be 

 studied, we have obtained effects in both the cord and the mixed nerve, following 

 similar excitation of the cortex, and by comparing the result of these observations 

 together have found that the excitatory state evoked by cortical activity undergoes 

 a diminution of over 80 per cent, in the passage from the cord into the sciatic nerve. 



We have also applied the galvanometric method to differentiate the cortical excit- 

 able areas, by recording and comparing the discharges from the same in the spinal 

 cord, and have found a striking degree of localisation demonstrated thereby in the Cat 

 as well as the Monkey. (See Chapter V.) 



(3.) Effect in the Spinal Cord on Excitation of the Corona Radiata. 



By a comparison made between the amounts of the electrical effects produced 

 in the spinal cord and the mixed nerve respectively after excitation of the corona 

 radiata, we found that the cord effect is four times as great as that in the nerve, and 

 further, that this corona-radiata-to-cord effect is little more than half the complete 

 cortex-to-cord change. (See Chapter VI.) 



(4.) Bilaterality. 



By comparing the records of the extent of the electrical effects in each half of the 

 longitudinally divided cord, and in the mixed nerve of each side, we have made fresh 

 observations on the important and complex question of bilaterality of representation 

 in the central nervous system. We have found 



(a.) That it is possible to obtain strictly unilateral effects in both the spinal cord 

 and sciatic nerve with complete excitation of both cortex cerebri and corona radiata. 



(b.) That the circumstances which favour the production of bilateral effects are 

 such as bring into play other portions of the central nervous system, e.g., the opposite 

 excitable cortex, cerebellum, and basal structures ; and, 



