ON THE MAMMALIAN NERVOUS SYSTEM. 287 



was to be made, an additional precaution was adopted to ensure its accuracy, the 

 cord being fixed by a fine needle. 



In some instances it was desirable that such intervening localised sections* should 

 be made some weeks previous to the actual experiments. This notably increased the 

 labour of the research, but is an essential control to such an experimental enquiry as 

 the present one. The animal was in all instances etherised and the seat of operation 

 having been carefully shaved, disinfected, &c., the necessary exposure and section were 

 then made under all aseptic precautions ; the wound uniting by first intention when 

 treated in the manner described by one of us in previous experiments of this kind. 



In conclusion, it may be pointed out that since almost each experiment involved 

 exposure, &c., of several different portions of the central nervous system, we adopted 

 the plan of performing these slowly, taking at least an hour or more in the preliminary 

 operative part of the experiment. We found that in this way less general shock 

 occurred than when the various parts were rapidly prepared one after the other. 



SECTION 3. RECORDING AND EXCITING APPARATUS. 



The recording and exciting apparatus used in the present research was chiefly that 

 adapted for determining the comparative amounts of the electrical changes in the 

 spinal coi-d and nerves at rest and when subjected to an excitation of definite intensity 

 and duration. 



The apparatus and its arrangement will be best indicated by separating it into the 

 following groups : 



(1.) The apparatus used in connection with the observation of the electrical changes. 



(2.) The apparatus used in connection with the excitation. 



(3.) Extra apparatus used for determining the characters of the muscular contrac- 

 tions. 



1. The Electrical Apparatus for Observation. 



Both these instruments were used to indicate the electrical changes evoked in the 

 spinal cord and nerves. 



(a.) The capillary electrometer was made by Mr. G. J. BuRCH.t The mercurial 

 column was magnified about 300 times by the special microscopic arrangement 

 employed, and was sufficiently sensitive to show perceptible movements when con- 

 nected with a difference of potential of 10 o 6 Daniell ; its reaction was quick enough 

 to enable it to respond to a difference of y^ro Daniell when connected with that 



* The localisation of all points or regions of the cord 'exposed is expressed in terms of the body of the 

 vertebra, or intervertebral disc, opposite to which the section was made. We furnish in Appendix A the 

 topographical relations which the spinal segments bear to the superficial origins of the several nerves 

 from the spinal cord. 



f Proceedings of the Royal Society. 



