408 MESSRS. F. GOTCH AND V. HORSLEY 



excited, and a comparison of the amounts in the two columns would thus give a 

 rough estimate of their comparative number. 



In the Cat the effects up and down evoked by the minimal excitation of the 

 posterior column are 92 and 74, that is an average of 83 ; those similarly evoked by 

 minimal excitation of the lateral column are 42 and 55, giving an average of 48. 

 Hence we infer that the direct fibres in the Cat between the dorsal and lumbar 

 regions are nearly twice as numerous in the posterior as in the lateral columns. In 

 the Monkey similar averages are 31 for the posterior and 75 for the lateral ; hence in 

 this animal we infer that the direct fibres are at least twice as numerous in the lateral 

 as in the posterior column. 



In both animals &quot;minimal&quot; excitation of the anterior columns at one end of the 

 experimental tract evokes a doubtful effect at the other end, and we infer that there 

 are few, if any, directly continuous fibres leading in these columns between the mid- 

 dorsal and the lumbar regions. Indeed, the cord may be divided in its anterior 

 region* without in any way interfering with the production of electrical effects, either 

 on the peripheral or central side of the division. Further, the application of more 

 intense stimulation to the anterior columns although producing local movements evokes 

 no constant electrical effects, the only results ever obtained being either with the use of 

 considerable intensity of stimulation or with the animal but very slightly etherised. 

 In these last cases, the magnitude of the local movements renders any strict localisa 

 tion of the stimulus upon the deeply situated anterior columns impossible ; any results 

 obtained under such circumstances we therefore rejected as absolutely untrustworthy. 



It must be borne in mind that in all the preceding experiments a degree of 

 anaesthesia was used, with which no violent movements were caused by any of the 

 stimuli employed. How far the relations of one column to another can be detected in 

 the unansesthetised animal by the employment of similar methods to those now used, 

 does not seem to us a question likely to yield fruitful results by its attempted 

 solution. The nervous impulses generated by the direct stimulation of fibres are 

 undoubtedly far more intense in their character than those which form the flow of the 

 sensory and motor processes in the normal animal. This is especially true when the 

 fibres in the posterior roots and the cord are subjected to external stimulation, possibly 

 because some mitigating influence of the cells in the posterior root ganglion is removed. 

 Hence, when such external stimuli are used, it is desirable that these should be of the 

 weakest character consistent with obtaining definite results, and that the animal 

 should be in a state of narcosis sufficiently profound not merely to cause complete 

 insensibility to pain, but the abolition of all violent reflex movements. 



The conclusions as to the conduction of nerve impulses in the cord of the Cat and 

 Monkey, to which the study of the foregoing experimental details has brought us, are 

 only true when these impulses are generated in the mode hitherto employed, viz., that of 



* These experiments will be published in del nil in a later communication in which we sliall specially 

 deal with the anterior columns. 



