490 Dr. A. D. Waller. 



observable. The opposition between Engelmann's and Hermann's state- 

 ments is therefore not absolute enough to justify the statement that 

 Engelmann's variation is negative and Hermann's positive. The 

 difference of statement is one of degree only, Engelmann having been 

 more prominently impressed by the outgoing phase, Hermann by the 

 ingoing phase. Hermann considers that the chief (ingoing) phase is 

 due to glandular activity, while the preliminary outgoing phase is 

 due to a short circuiting, via gland ducts, of an epithelial current of 

 action attributable to keratinisation. 



Bach and Oehler,* under Hermann's guidance, observed that super- 

 ficial cauterisation of the skin with saturated solution of HgCl2 abolishes 

 the normal current, and leaves the action current intact. Hermann's 

 view is that normal current depends upon epithelial investment as well 

 as upon glandular epithelium, whereas action currents through nerve 

 stimulation depend upon glands. 



Bayliss and Bradford,! employing Hermann's nerve-skin preparation, 

 found Hermann's variation (ingoing) during January, Engelmann's 

 variation (outgoing) during March. Their attention was particularly 

 attracted during the last three months of the year to a triphasic 

 character of variation - + - (or, according to the terminology of the 

 present communication, + - +). 



Direct Excitation of the Skin. — The first mention of definite direct 

 excitation of the skin is to be found in Engelmann's paper of 1872. | 



Strong induction shocks were passed through the electrodes applied 

 to opposite surfaces of the skin. 



Compensation of its current was previously established, the galvano- 

 meter was cut out of circuit during excitation, and the effect upon the 

 skin was observed immediately afterwards. The direction of excitation 

 was not distinguished. 



Biedermanng approaches the question from the general standpoint of 

 Hering's theory of opposite movements, dissimilation and assimilation, 

 employs more particularly the frog's tongue, finds that during direct 

 tetanisation (tongue and galvanometer in series) the response of the 

 living tongue may be either positive or negative according to circum- 

 stances, the principal of these being temperature and moisture. 



Bohlen,|| under Biedermann's guidance, studied the gastric mucosa, 

 i.e., one epithelial layer in place of two, as in the case of the tongue, 

 and obtained results confirmatory of Biedermann's. 



Keidll and Reid and Tolput,** using the skin of the eel, found that 



* ' Pfliiger's Archiv, vol. 22, p. 30, 1880. 



f ' Jour, of Physiology,' vol. 7, p, 217, 1886. 



X 1 Pfliiger's Archiv,' vol. 6, p. 136. 



§ ' Pfliiger's Archiv,' vol. 54, p. 209, 1893. 



|| ' Pfluger's Archiv,' vol. 57, p. 97, 1894. 



1" ' Phil. Trans.,' B, 1893, p. 359. 



** ' Jour, of Physiology,' vol. 16, p. 217, 1894. 



