1891.] On the Mammalian Nervous System. 237 



e'ectrical condition of the fibres in the cord tract, and that, with a 

 suitable apparatus for responding to such changes, these might be 

 both ascertained and recorded. The accomplishment of a further 

 purpose, viz., the localisation of both paths and centres by ascertaining 

 the excitatory electrical effects in relation with them, was one of the 

 main objects we had in view. In carrying it out, we found it was 

 unnecessary to employ the electrometer, and, in fact, that it was ad- 

 vantageous to use the galvanometer, the record of which would be 

 more easily and more accurately noted, since its graduation admits of 

 far higher magnification. Moreover, with this instrument it was 

 possible, by employing a series of stimuli, of known number and 

 duration, to obtain quantitative results of definite comparative value, 

 as will be shown further on ; and thus, to compare both the size of 

 different central paths and the amount of nervous energy discharged 

 along the same path from different sources. 



The plan upon which the full paper is framed is, first, to give an 

 historical retrospect of the work of authors who have opened up the 

 study of electrical changes in the central and peripheral nervous 

 system ; second, to describe at length our mode of experimentation, 

 rith special reference to the modifications which we have introduced, 

 len to compare roughly the results we have obtained by our present 

 lethod with those which had been previously ascertained by the 

 iphic method, and so introduce the description of the facts which 

 have discovered, elucidating the physiology of the spinal cord, both 

 its relation to the higher centres and to the peripheral nerves. 



2. Experimental Procedure. 



The observations were in all cases made on etherised animals (cat 

 id monkey), with due regard to the special influence of the anaes- 

 letic. The operative procedure was so designed as to provide for 

 litable exposure of a particular region of the nervous system for 

 excitation, and of another part in which the electromotive changes 

 evoked by the stimulation may be observed. The relative parts were 

 follows : 



Part eiposed for Excitation.. Part exposed for Observation. 



Brain (cortex and corona radiata). . - . and spinal cord. 



Do. do. do. .... and mixed nerve. 



Spinal cord and spinal cord. 



Do and mixed nerve. 



Mixed nerve and spinal cord. 



Spinal roots do. do. 



Posterior roots and mixed nerve. 



The excitation was either electrical, chemical (i.e., with absinthe 

 id strychnine), or mechanical. In the former instance the duration 



