ON THE MAMMALIAN NERVOUS SYSTEM. 339 



&c.), which arouse the neighbouring cortex cerebri, and cause a discharge from cor- 

 puscles in which the peripheral part under investigation is yet represented. 



We have little doubt but that this is the true explanation, and believe that 

 excitation really limited to the fibres of the corona radiata is never followed by such 

 an after-effect. This will, however, be again referred to in Chapter VII. 



2. Electrical Changes in the Sciatic Nerve. 



As in the result of cortical stimulation, so in that of excitation of the corona radiata, 

 there is a striking difference between the effect in the cord and that in the sciatic 

 nerve. We have never yet observed any effect from the nerve when the electrometer 

 was employed ; in the galvanometer, however, such effects are generally seen, although 

 the necessary stimulus has to be so strong as to run the risk of evoking discharge 

 from the uninjured portions of cortex. Whenever such epileptic discharges obviously 

 occurred, as evidenced by the muscular movements, the observation was regarded as 

 worthless. 



The following table gives the results observed in eight Cats, all those being 

 excluded in which, owing to the degree of anaesthesia being less, the excitation 

 brought about general muscular movements. 



As in the case of cortical excitation, so here, the deflections observed in the (corre- 

 sponding) nerve on the opposite side to that of the excitation are placed in a separate 

 table to those observed in the nerve on the same side, the latter being given so as 

 to show when bilateral effects were produced. 



It will be seen that the amounts vary between 4 and 68, and that the average of 

 all readings is 26. 



2x2 



