ON THE MAMMALIAN NERVOUS SYSTEM. 349 



sented in the excitable cortical areas of each hemisphere. The question, therefore, 

 narrows itself down to that as to whether the highest, i.e., purposive, movements of 

 the limbs of both sides of the body are represented in the cortex of one and the same 

 hemisphere. Theoretically, we are compelled to admit (following the teaching of 

 HUGHLINGS JACKSON) from the evolutionary standpoint such bilateral representation 

 of the limbs. The important point for experiment to decide, however, is whether such 

 bilateral cortical representation exists in more highly differentiated animals to a suffi- 

 cient extent to cause movements. The opinion of most authors is evidently that it 

 does so exist. We feel, however, very strongly that the methods hitherto adopted by 

 these authors are not definitive, and do not establish the positions claimed. We are led 

 to this conclusion from the consideration of certain facts now to be discussed which have 

 come under our notice in the present research, as well as of others previously dis- 

 covered, the importance of which has of late become more recognised. By welding 

 the fresh information, which the use of our method has given, to the old, we hope to 

 help forward the solution of this apparently simple but very complex subject. 



(1.) Narcosis. As is seen from the foregoing retrospect, some authors have employed 

 narcosis to a greater or less degree. The statement that a narcotised cortex could in 

 any way " completely discharge " is always, of course, open to objection, and hence 

 observations in animals narcotised to unconsciousness have been held by some to be 

 incomplete. The answer to this objection, however, is simple and, we believe, 

 sufficient ; it is included in that of the next paragraph, in which " complete discharge " 

 of the efferent apparatus of the cortex is seen to be effected even in unconsciousness. 

 Clinical experience of epilepsy also affords evidence of the truth of this contention. 



To look at the question from the opposite standpoint, although electrical excitation 

 of the cortex is not in any way painful, still it is clear from observation of the 

 influence of such stimuli in imperfect narcosis that the effect spreads rapidly from centre 

 to centre, i.e., to the opposite hemisphere, &c., and hence renders any topographical 

 conclusions impossible. 



The observations, therefore, which have been made in this way, though very 

 valuable as throwing much light on synchronous excitation, e.g., in epilepsy, &c., 

 cannot, as yet, form a basis for the determination of the presence or absence of 

 bilaterality of representation so far as the limbs are concerned. 



(2.) An adequate stimulus ivhich completely discharges the cortex at one given focus 

 of representation of one limb produces movement in that limb only and none in the 

 limb of the same side. 



By the term " adequate stimulus ivhich completely discharges the cortex " at one 

 given spot, we mean an interrupted induction current of sufficient strength to evoke 

 a strong movement in the limb represented (in the present research the leg), and to 

 produce a slight excitation also (by overflow of nerve impulses) of the nearest lying 

 centre or focus, which in our experiments was naturally that for the fore or upper 

 limb. If the strength of the stimulus and the condition of the cortex be accurately 



