On Skin Currents. 



481 



with or against a reaction of low E.M.F., and is not eluded as easily as 

 might have been anticipated by the use of alternating currents. Thus, 

 e.g., while it is easy to assure oneself that a healthy skin may survive 

 for at least a week, one may not feel assured that it is absolutely dead 

 at that time ; and in the case of skin obtained from the post-mortem 

 room 24 hours after death, while one may be quite sure that a given 

 skin is still alive, one may not be so sure that another skin is com- 

 pletely dead. 



For these reasons I have preferred in the present communication to 

 describe only the very clear and easily demonstrated results of direct 

 excitation of the frog's skin. And in connection with those clear and 

 regular results, I take the opportunity of describing the more variable 

 and debateable results of the indirect excitation of the same skin 

 through nervous channels. 



Method. — The method b}^ direct excitation is as has been previously 

 described and figured in the case of a vegetable tissue,* a piece of 

 frog's skin laid on a perforated glass or ebonite plate in place of the 

 seed between the unpolarisable electrodes, which serve for the exciting 



current and subsequently for the excited current. For the purposes of 

 the description to follow, the skin is to be pictured as if with its superior 

 or external surface A directed upwards, in which case a current from 

 the internal surface B to the external surface A, or an "outgoing" 

 current is ascending or positive, and an " ingoing " current from A 

 to B descending or negative. Excitation was made by single induction 

 shocks, by series of alternating induction shocks, and by condenser 

 discharges. The direction of exciting currents was always determined, 

 the effects of polarisation were tested for, the electrodes in particular 

 being always examined for polarisation, " anomalous " or positive, as 

 well as ordinary or negative. 



* A. D. W„ loc cit, p. 82, fig. 1. 



2 M 2 



