450 MESSRS. F. GOTCH AND V. HORSLEY 



to the trunk of the nerve. It was notably affected by several conditions, of which 

 the most important are those affecting the state of the animal and those connected 

 with the intensity of the stimulus. The influence of these two conditions demands 

 closer examination. 



The state of the animal has tlie greatest influence on the amount of the change. 

 To take the most powerful factor first, the systemic death of the animal, this is at 

 once shown in the diminishing size of the effect, until, in about ten minutes, no 

 electrical change can be evoked in the nerve when the cord is excited. 



The following experiment may be quoted in illustration of this point ; it is one in 

 which the posterior root instead of the nerve was observed. 



The cord of a Cat was divided at the 10th dorsal and the cauda equina exposed. The 

 7th lumbar posterior root on the left side was then ligatured and divided near the 

 ganglion, raised in air and its central end and surface connected with the galvano- 

 metric electrodes. 



Excitation for five seconds of a given tract in the cord (the left posterior column) 

 evoked an electrical change indicated by a galvanometric effect of 253. The animal 

 suddenly died from collapse, the heart failing, and the experiment was then repeated 

 about four minutes after death, when the deflection was found to be less, viz., 1G5. 



The time of this observation was 12.1. A series of such observations were then 

 made as follows : 



Time. Deflection. 



12. 1 165 



12. 2 142 



12. 3 139 



12. 5 75 



12. 7 50 



12.10 8 



12.12 nil 



Excitation of the root itself still evoked considerable effects at 12.15. We have 

 often had the opportunity of noting that the nerve electrical effect when evoked by 

 excitation of the cord, disappears on death earlier than when evoked by excitation of 

 the nerve trunk. This we imagine to be due partly to the circumstance already 

 mentioned that the latter excitation produces normally a more marked effect than 

 the former, and partly to the changes in excitability which, in accordance with the 

 Hitter -Valli law, proceed from the centre towards the peripheral attachment of a 

 nerve. 



A more important influence than this of death, since it is one present throughout 

 all the experiments, is that dependent upon the varying degree of anesthesia. There 

 are many experiments which furnish illustrations of this point. A stimulus of the 

 same character, intensity, and duration, applied to the same region of the cord, evokes 



