ON THE MAMMALIAN NERVOUS SYSTEM. 



331 



the galvanometric effects display, as might be expected, great inequalities ; these, 

 however, will be seen to be in strict relation with the amount of visible contraction 

 evidenced in the muscles of the trunk, &c., and hence are really determined by the 

 force and duration of the cortical discharge. Bearing this in mind, the following 

 table is very instructive, as indicating the size of the deflections, which vary, as is 

 seen, from 63 to 510 scale. The intensity of the stimulus, the particular cortex 

 excited, and the character of the fit evoked, are in each case noted. 



It will be seen that the average of these readings, which were all taken in four 

 animals (Cat), as far as possible under similar conditions of etherisation, &c., amounts 

 to 193 scale. It will be also seen that it is always easy to produce by a sufficient 

 intensity of stimulation readings which are in excess of this. 



GALVANOMETRIC Effects produced in Spinal Cord of Cat by Cortical Excitation. 



The interest of the results will increase when we compare the average amount with 

 the highest obtainable value of the galvanometric reading afforded by the effect of 

 cortical excitation in the sciatic nerve. It must be now pointed out that in all cases, it is 

 essential to reject observations in which there are sudden irregular changes in the resting 

 electrical difference of the cord, since these are in great measure due to slight failure 

 of the anaesthesia and to the consequent semi-voluntary discharge of cortical impulses. 



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