378 



Dr. A. D. Waller. 



[Mar. 17, 



of living skin, the influence of single shocks (and still more of alterna- 

 ting currents) is considerable, and must be reckoned with in any 

 estimate of voltage. In, e.g., skin No. VII (vide Tabular Summary), the 

 difference between the responses in the two directions of tetanisation 

 at 10,000 units on the second and third days depends on the fact that 

 the order of tests was reversed on the two days. For this reason, in 

 any comparison between the effects of excitation in opposite directions 

 one pair of trials is insufficient : two or more pairs of trials are neces- 

 sary. In fig. 1, e.g., the result of two pairs of trials is given. In 

 fig. 4204 the decline of voltage is, in reality, much greater than is at 

 first sight apparent, by reason of the augmented conductivity aroused 



I E I ! 



o io 20 30 m in. 



Fig. 3 (4204). — Same skin 22 hours after excision. Series of 16 positive responses 

 to tetanisation for 8 seconds at intervals of 2 minutes. Coil at 1000, supplied 

 by 8 L. Make — , Break +. Gradual decline of E.M.F.; which decline is 

 greater than apparent by reason of increasing conductivity; the latter, as 

 sbcvrn by the standard deflections at beginning and end of experiment, has 

 been more than doubled. 



by the succession of excitations. For the same reason it is not easy to 

 make satisfactory observations of the variation in strength of response 

 with variation in strength of excitation, even when the mean of succes- 

 sive effects is taken on ascending and descending scales, the influence 

 of fatigue remains obvious, especially if (as ought to be done) the 

 gradual increase of conductivity is taken into account. 

 For example : — 



