OX THE MAMMALIAN NERVOUS SYSTEM. 445 



are either not equally numerous, or are not equally easy of passage ; the posterior 

 column of the same side offers special facilities for the passage of the impulses, the 

 lateral column of the same side offers facilities greater than the posterior column 

 of the opposite side, but both, whilst far inferior in this respect to the posterior 

 column of the same side, are far superior to the remaining lateral column of the 

 opposite side. This last, at least in the narcotised animal, offers practically no 

 facilities for such passage. 



It is, perhaps, unnecessary to draw attention to the circumstance that the above 

 results are only verified in the case of "the lower dorsal region of the cord in the Cat, 

 and to some extent in the Monkey. 



The principal deficiencies of the present method have been indicated in this and 

 previous chapters, but may now be summarised. They are connected 



(a.) With the character of the nerve impulses, which, being due to electrical 

 excitation, are more intense, and possibly different in quality, to those which are 

 generated in peripheral sensory end organs. 



(b.) With the necessity of insulating the observed portion of cord, to ensure the 

 observation of localised effects in it, this being accomplished by a severe operation 

 which entails the death of the animal at the close of the experiments. 



(c.) With the limited anatomical scope of the method as at present used, the highest 

 point which we have reached being the mid-dorsal region. The shock of the exposure 

 above this has rendered our experiments, carried out higher than this, unsuccessful. 



The chief merits of the method are - 



(a.) That the changes investigated are the electrical excitatory processes in the cord 

 itself severed from the encephalon, and are free, therefore, from admixture with 

 cerebral effects, and are independent of the reflected outcome of such effects in the 

 muscles. 



(b.) That the changes are so definite as to admit of comparison as to their quantity, 

 and thus of a quantitative estimate of the nerve energy transmitted in the cord 

 under different' conditions. 



(c.) That this quantitative character of the results enables a comparison to be made 

 of the effects of nerve energy which are dependent respectively on the integrity of the 

 different parts of the cord. 



The conclusions to which we have thus arrived will receive additional confirmation 

 from the results of experiments in which the impulses in the nerves are made the 

 subject of investigation by the electrical method, such impulses being ai-oused by 

 excitation of the different columns in the cord. 



These will be detailed in the next chapter, at the end of which a general review 

 of the whole question of conduction in the cord, as elucidated by our method, will 

 be given. 



