1877.] 



Excitability of Motor Nerves, 



213 



throw in the entire resistance of which the tube was capable, i. e. a greater 

 resistance than could possibly be required to cause minimal stimulation 

 in the next stage of the experiment. I now cut the gastrocnemius through 

 at its extreme femoral end ; and the same instant that I did so I began 

 rapidly to pass the sliding rods down the U-tube with one hand, while 

 with the other hand I closed and opened the current a number of times 

 in as rapid succession as possible. Having observed the point at which 

 the responsive contraction was first given, and throwing away that par- 

 ticular muscle, I repeated the experiment with another muscle, and so on 

 — never ushig the same muscle for more than one such observation, and so 

 always obtaining a record of the maximum increase of excitability imme- 

 diately after infliction of the injury. 



The results of a number of experiments conducted on this improved 

 method confirm, in the main, those previously obtained. As before, how- 

 ever, I encountered immense individual variations in different muscles, 

 and therefore, as before, I here select mean cases for quotation. It is 

 only necessary further to explain that in the appended Table the figures 

 represent the number of Ohm's units of resistance which, with two Grove's 

 cells, I required to introduce in each of the eight cases before I procured 

 minimal stimulation. 





Anodic 

 make. 



Kathodic 

 make. 



Anodic 

 break. 



Kathodic 

 break. 



Before cutting .... 

 After cutting 



90,000 

 140,000 



100,000 

 300,000 



14,000 

 195,000 



6,000 



14,000 



These proportions, as already observed, agree pretty closely with those 

 which I obtained by the method previously employed. Such differences 

 as exist are to be explained, partly by the superiority of the later method, 

 and partly by the fact that in the one series of experiments I employed 

 Rana temporaria, while in the other series I employed R. esculenta — the 

 muscles of the latter species being less excitable than those of the former. 

 It is interesting to note that the chief difference in the two series of 

 results has reference to the katkodic make, and that the difference is of 

 such a kind as to render the degree in which the excitability is increased 

 by section in this case more proportional to the degree in which it is 

 increased in the case of the anodic break. The two cases, however, are 

 still very far from being numerically proportional, the degree of increase 

 in the two cases being respectively represented by the numbers 1 : 3 and 

 1 : 14 (nearly). To explain this numerical discrepancy, therefore, we must 

 still resort to the considerations set forth in my previous paper (see vol.xxv. 

 pp. 12, 13). I may here add that in some instances of maximum increase 

 of excitability, due to nerve-injury, I have observed thekathodic make to 



