v ELECTROMOTIVE ACTION OF EPITHELIAL AND GLAND CELLS 491 



influence of the initial force of the incoming current upon the 

 excitation effects is apparent. The threshold of excitation 

 actually lies, as a rule, much higher than in the throat mucosa. 

 Before there is any definite effect in one or the other direction, 

 there will often he an uneasy oscillation of the magnet, giving 

 the impression that two antagonistic effects are in conflict. 

 With weak currents the deflection of the positive variation 

 finally preponderates, while with very closely approximated, or 

 closed -up, coils, the contrary is the case without exception. 

 A short, positive fore-swing is often to be seen, after which 

 occurs the much stronger negative variation. At the end of 

 the excitation the latter nearly always declines rapidly and 

 completely. In several cases in which the entering rest 

 current exhibited an unwonted intensity, there were, from 

 the weakest effective currents to the strongest, only pure 

 monophasic negative variations, which then attained proportions 

 that are usually seen in the tongue only, under similar 

 conditions. Thus, in one case, the cloacal mucosa of a non- 

 curarised Ii. temporaries, stretched over a cork frame, and led off 

 from both surfaces, exhibited an incoming current of such 

 amplitude that the scale flew off; after compensation there 

 was, even with the coil at 180, a distinct, negative variation of 

 several degrees of the scale, and with the coil at 100 the 

 scale vanished on excitation. Unlike the throat mucosa, the 

 deflection, apart from small oscillations, remained tolerably 

 constant so long as the excitation continued, after which it 

 declined rapidly. Where the cloacal mucosa, as seems always 

 to be the case if there is no fluid secretion, is currentless, 

 or weakly active in an ingoing direction only, the strongest 

 tetanising with the coil pushed home produces no visible 

 negative variation ; there is either no effect or at most a weak 

 deflection in the sense of an ingoing current. This shows that 

 the excitation effects depend upon the mucosa itself, and are 

 not caused by the muscles lying beneath it. 



In the richly glandular skin of Amphibia, the results of 

 direct and indirect excitation are essentially similar. Engel- 

 mann (I.e. p. 136) carried out experiments in which pieces of 

 skin (E. temporaria) were excited by single make or break shocks 

 from an ordinary induction apparatus, the induction currents 

 being led in by the leading -off electrodes. At the moment 



