ON THE MAMMALIAN NERVOUS SYSTEM. 337 



EXCITATION of Lumbar Cord. Electrical Effect in Dorsal Cord. 



Cat. Average effect evoked in the Cat by stimulation of one lateral column. 



Mimimal stimulation 55 



Maximal ,, 124 



Average effect evoked in the Cat by stimulation of one posterior column. 



Minimal stimulation 74 



Maximal ,, 164 



Monkey. Average effect evoked by stimulation of one lateral column. 

 Maximal stimulation 133 



Average effect evoked by stimulation of one posterior column. 

 Maximal stimulation 86 



The chief differences between these results obtained when nerve impulses proceeded 

 up the cord and those obtained when they travelled down, are the following : 



(1.) The maximal effect in the Cat is more than twice as great as the minimal with 

 stimulation of both lateral and posterior columns when the impulses are ascending, 

 i.e., the lumbar end excited. On the other hand, when the impulses are descending 

 the maximal effect was less than twice as great. There is thus a gain in the amount 

 of the effect, when the stimulus is on the lumbar side of the region, in proportion 

 as the excitation increases in intensity. 



(2.) The minimal posterior column effect with ascending impulses is larger than 

 the lateral in the Cat in the proportion of 3 to 2, but this proportion is less than that 

 obtained when the dorsal cord was excited and descending impulses evoked, since this 

 was 2 to 1. 



(3.) In the Monkey the lateral column effect is larger than the posterior in the 

 proportion of 3 to 2, when ascending impulses are evoked by maximal stimulation ; 

 with descending impulses similarly evoked the proportion is 9 to 7. 



The characteristic predominance of the lateral column of the Monkey is however 

 marked, whether the excitation is dorsal and the descending impulses investigated, 

 or lumbar as in the present case, and the ascending effects observed. 



The differences above described seem to indicate that the generated impulses travel 

 not only along direct but indirect paths, that is along paths involving cells, and that 

 the structural relations and physiological effects of the interposed structures are such 

 that these influence, in both animals, traversing nerve impulses differently according 

 as their direction is centripetal or centrifugal. It is particularly as regards the 

 lateral column effect that this influence of direction is most marked ; it would, 

 therefore, seem that the lateral column comprises among its fibres some (presumably 

 iriternuncial) which ofl er less resistance to ascending than to descending impulses. 

 This view will receive confirmation, and be again referred to in the later experiments 

 on the relations of the cord to the nerves. (See Chapters IX. and X.) It is sup- 



3 D 2 



