v ELECTROMOTIVE ACTION OF EPITHELIAL -AND GLAND CELLS 495 



a tolerably rapid deflection (in the positive direction) is developed, 

 but remains for the most part stationary, after which a slow 

 further growth continues to the maximum. If the excitation is 

 protracted, there will usually be reversal, and slow return ; if 

 interrupted at the height of its deflection, the scale will remain 

 at the point of deflection for some time longer, or else continues 

 its course a little further, returning then more slowly than the 

 variation, to its original position." Hermann observed the same 

 positive deflection after very short excitation : " At the end of 

 such excitation the scale remains at rest for a certain time, and 

 then pursues its deflection in the positive direction, though the 

 variation is much less than with sustained excitation." Thus 

 there is a complete antithesis between Hermann's results and the 

 earlier conclusions, which is but little modified by the more 

 frequent appearance of a " negative fore-swing " on the skin of 

 the lower limb. Both Eoeber and Engelmann have observed 

 pure positive effects of excitation on the preparation last men- 

 tioned, although quite exceptionally and under conditions in 

 which it is questionable whether the phenomenon is to be re- 

 garded as " normal." This was the case, e.g., where the prepara- 

 tion, after being uncovered for some time in a moist chamber, 

 exhibited " excessively weak " (entering) currents, and soon 

 ceased to be excitable. Later on Bach and Oehler (81) found 

 under Hermann's direction, in the first place, that the negative 

 variation of the entering rest current of the skin was entirely 

 dependent upon the strength of the latter (a fact to which we 

 have frequently referred above), and on the other hand that in all 

 cases where, whether through warming beyond a certain limit, 

 or painting the skin with strong salt solution, the " current of 

 rest " was perceptibly weakened, its negative variation declined 

 rapidly, finally giving way to " an incoming secretion current," 

 i.e. a positive variation. From this we may assume that in 

 Hermann's experiments, frogs were used in which the skin current 

 was very little developed. In the meantime he has made recent 

 experiments (82), showing that in certain cases there is, even 

 with a strongly developed, entering, rest current a mainly or 

 exclusively positive variation, when the nerves of the skin are 

 excited. This may be demonstrated on the skin of the leg in the 

 tree frog, as well as on the skin of the salamander (Proteus 

 anguineus). 



