338 



MESSES. F. GOTCH AND V. HORSLEY 



EFFECT in Spinal Cord. 



We would pass from this part of our subject, since our knowledge of the process 

 of secondary degeneration has shown that in the arrangement of the experiment all 

 we do is to observe at one (the spinal) end of a column of fibres the changes evoked 

 by stimulating these fibres at the other (corona radiata) end, were it not that the 

 above effect is capable of modification in a manner which demands consideration. 

 Moreover, we wish to emphasise the fact, that in its simplest form the corona radiata 

 effect, as observed in the cord, is an example of the application of the galvanometric 

 method to the determination of directly continuous nerve tracts in the central 

 nervous system. This, as we shall see later in dealing with the spinal cord itself, is 

 one of the most valuable uses to which the method can be put. Thus when a definite 

 tonic effect, and that only, is evoked by the excitation, the application of the stimulus 

 to any fibres of the corona radiata, except those immediately underlying the focus of 

 representation of the movement of the lower limb, produces no electrical changes in 

 the lower dorsal cord, even though the muscles of other parts are sent into tonic 

 contraction. The modifications we have referred to above, are those which have been 

 observed by most workers with the graphic method, and consist in the presence of an 

 after-effect in no wise differing from the clonic stage of the full cortical discharge save 

 in duration and completeness. The assumption is naturally that in the arrangement 

 of the experiment, it is impossible to avoid exciting association fibres (fibrse arcuatae, 



