308 



Dr. A. D. Waller. Effect of Heat upon the [Feb. 20, 



after-effect is negative. The muscle is then scalded, and submitted to five 

 successive glows as before ; when a smaller deflection in the positive direction 

 occurs at each glow. It is presumably a physical (thermo-electric) effect. 



II. The nerve record consists of three successive effects of three successive 

 glows under B, followed by four successive effects of four successive glows 

 under A. In the B group the first response is positive, the second is small 

 positive followed by large negative, and the third is negative. In the A group 

 the first (positive) response is the largest, the second (positive) is smaller, the 

 third is smallest and gives place to a deflection in the negative direction, due 

 to injury, the fourth is a small negative deflection. 



III. The skin record consists of two groups of four successive responses ; in 

 the first group the external surface, in the second group the internal surface, 

 of the skin is led off to the galvanometer. In the first group, each response 

 at B is relatively large and the current is directed in the skin from B to A 

 (" ingoing " current, or B zincative). In the second group the responses are 

 hardly perceptible. 



In muscle (and in nerve), where the electrical effect of local excitation is 

 " negative," the effect of moderate heat is " positive." 



In the skin, where the electrical effect of local excitation is " positive," the 

 effect of moderate heat is " negative." 



Excessive heat, producing injury, gives a " negative " effect in muscle (and 

 nerve), a " positive " effect in the skin. 



N.B. — " Negative " = " Zincative." " Positive " = " Antizincative." 



To my understanding, the expressions " positive " and " negative " are 

 ambiguous without this specification, and the description given in the text in 

 terms of " positive " and " negative," while correct, is very confusing. 



The general conclusion from all these experiments is that the first electrical 

 effect of moderate local heat is of opposite direction to that of local excita- 

 tion and of local excessive heat, i.e. that the effect of moderate heat is 

 " anti-excitatory." 



{Postscript {added May 27). — In consequence of a question put to me at 

 •the conclusion of the demonstration that accompanied the above com- 

 munication, I have taken observations on the effects of gradual rise and fall 

 of temperature upon the normal (ingoing) current as well as upon the 

 electrical response of the frog's skin. The alterations of temperature were 

 brought about by gradually warming and cooling a metal box containing 

 the skin and electrodes, the thermometer giving the temperature of the air 

 in the box. 



With rising temperature the electrical response of the skin increased at 



