ON THE MAMMALIAN NERVOUS SYSTEM. 399 



rupted lateral, then the preponderance of the effect evoked by the left posterior 

 column would show that such indirect communication between the fibres in the 

 posterior column and those in the lateral consists chiefly of posterior column fibres, 

 which do not cross the cord. It may indeed be doubted whether the small effects 

 evoked by excitation of the lateral and posterior columns of the side opposite the 

 uninterrupted lateral are any evidence of veritable crossing nerve impulses, since it is 

 probable, that with the strength of stimulus used (2000), the excitation of any 

 column may cause reflex discharges from the cells in the grey matter of the upper 

 dorsal portion of the cord, and the effect transmitted by the uninterrupted lateral 

 would therefore be due to spread of the awakened activity involving the cells which 

 are connected with its own internuncial fibres, and which thus send forth nerve 

 impulses to be transmitted down the uninterrupted channels. 



However this may be, there is no indication by this electrical method of any large 

 indirect crossed path, in connection with the lateral column, of fibres such as would 

 conduct nerve impulses downwards from the dorsal to the lumbar cord. The interest 

 which attaches to this negative result hangs upon the presumed connection of the 

 lateral* tract with nerve fibres on both sides, and upon the circumstance that it 

 forms the first of a series of results all pointing conclusively in the same direction, 

 which will be set forth in Chapters IX. and X. 



(2.) Electrical Effects Evoked in the Dorsal Cord by Excitation of the Lumbar 



Cord, after intervening Sections. 



A. Influence of Hemisection. 



Since the characters of the normal electrical effects in the cord are not the same 

 when the nerve impulses are ascending, i.e., evoked by excitation of the lumbar 

 region, as when descending, i.e., evoked by excitation of the dorsal region, it is not 

 surprising that the influence of intervening lesions upon the former group of effects 

 should differ from the influence already described upon the latter group. 



The influence of hemisection upon ascending changes was studied in two animals 

 (Cats), one with minimal, the other with maximal stimuli, the experimental tract 

 being situated as shown in the following table, and the hemisection made on the left 

 side at the level of the 13th dorsal and lOth-llth dorsal vertebrae respectively. 



* MIESCHER, 'Arbeiten ans dem Pliysiologisehen Institut in Leipzig,' von C. LtJDWro ; WoROSCHlLOFF, ibid. 



