150 E. A. Schäfer, 



gyrus and occipital lobe. But when any of these parts are removed 

 the lesion is not followed by motor paralysis. 



It was therefore inferred by Ferrier that there must be a funda- 

 mental difference between the two regions of the cortex, and that this 

 difference is probably of such a nature that the excitable parts grou- 

 ped under the first head are directly in connection with centripetally 

 conducting fibres of the motor tract, and produce movements by trans- 

 mitting impulses directly along that tract, whilst the movements which 

 are produced when those grouped under the second head are excited, 

 are the result of a subjective sensation set up as the result of the 

 excitation of the nerve cells, and producing the same effect as if a 

 sound were heard by the opposite ear, or a light seen as if flashed 

 from the opposite side, viz: a movement of the head and eyes in the 

 direction of the apparent sound or sight respectively. Others, on the 

 other hand, have taken up the position that in all cases, whether the 

 excitation is applied to the motor or to the sensory regions of Ferrier, 

 the movement is the result of subjective sensations; that in the case 

 of parts belonging to the first head the sensation which is thus sub- 

 jectively excited is the muscular sense, and removal of the part pro- 

 duces paralysis by abolishing that sense. 



The question is however capable of being put to the test of ex- 

 perimental measurement. If the actions produced by excitation of both 

 regions — we may call them simply motor and sensory for the sake 

 of brevity and clearness of description — are produced in both cases 

 directly by nerve impulses transmitted along the motor tract, or are 

 produced in both cases only indirectly through some other centre (in 

 the basal ganglia or elsewhere) whence the nervous impulses pass to the 

 motor tract, then, if the period of latent excitation of the muscles moving 

 the eyes be accurately measured, it should be about the same in both 

 cases. Whereas, if in the one case the transmission of impulses is di- 

 rect, and in the other indirect, there should be a marked difference 

 in the latent periods of the two, for the nervous impulses have in the 

 one case to be transmitted through at least one centre more than in 

 the other. This point I have accordingly endeavoured to determine. 

 The method of experimentation was as follows : 



