354 



MESSRS. F. GOTCH AND V. HORSLEY 



just mentioned, viz., 5000, the left cord was then connected with the galvanometer ; 

 excitation of the right hemisphere (i.e., that of the corresponding side) gave 375 degrees, 

 and excitation of the left hemisphere (i.e., that of the same side) only gave 8 degrees. 

 This mode of pairing the observations is clearly one likely to give the most useful 

 results, but we also paired the observations in the following way, viz., by connecting 

 first one side of the cord with the galvanometer and then the other, in each case 

 stimulating the same hemisphere. 



The foregoing two selected experiments illustrate the conditions which are observed 

 with the hemispheres in a normal state. Before considering the further evidence 

 afforded by massing our observations, we must draw attention to the greatest 

 difficulty in connection with this branch of enquiry, and which prevents us from 

 speaking so positively upon this point, when the results noted at the beginning of 

 any experiment are added to those recorded at the end. We refer to the great 

 tendency of the cortex to become hyperexcitable after one or two excitations, and, 

 consequently, for the excitatory state to pass from one hemisphere across to the other. 



This is especially liable to occur when through repeated excitation the cortex has 

 been thrown into a hyperexcitable state. This is, in fact, the objection which may 

 be urged against any conclusions derived from massing together results, many of 

 which being repetitions involve previous excitation. The same objection can also be 

 urged with equal truth against the results of most of the observations of earlier 

 experimenters ; but upon the question whether this objection accounts for the whole 

 of the results to be immediately given, we have no means of expressing any decisive 

 judgment. It is, however, easy to understand that a considerable proportion of the 

 bilateral effect noted in the two halves of the cord when all the results are taken 

 may be due to this circumstance. 



The average amount of the bilateral effect obtained in the two halves of the split 

 cord when one hemisphere is directly excited is as follows : 



Cat Average of 12 observations . . 

 Monkey Average of 31 observations 



Cord. 



Opposite half. 



157 



158 



Same balf. 



33 

 32 



It will be seen that when all results are averaged together there is an effect on 

 both sides of the cord, and that its amount in the half opposite to the excited cortex 

 is five times as great as that in the half which is on the same side. 



The close identity of the figures in the two animals is remarkable, and not what 

 our early observations had led us to anticipate."" 



* One of us (V. H.), however, had already shown by experiments with absinthe combined with 



