v ELECTROMOTIVE ACTION OF EPITHELIAL AND GLAND CELLS 493 



Our experiments show that the results obtained with indirect 

 excitation of the frog's skin from the nerve agree almost exactly 

 with those of direct excitation. Eoeber (I.e. p. 3) employed a 

 method by which he was enabled to experiment on the skin of 

 the leg without much injury to it, and this is to be preferred 

 to the preparation from the skin of the back used later on by 

 Hermann. Under all conditions it involves much less injury to 

 the skin, and, apart from the greater resistance of the prepara- 

 tion, makes it easier to test the effect of different reagents on the 

 phenomena of excitation. We can either use Eoeber's original 

 method, in which, after setting up an ordinary " rheoscopic 

 frog's leg," the skin " which covers the whole leg up to the knee- 

 joint is divided by a circular cut at the ankle from the inferior 

 portion, split up the anterior surface by a longitudinal cut, and 

 then prepared and turned back from the entire limb almost to 

 the knee-joint. The leg is then divided below the knee and 

 taken off, leaving only the sciatic nerve, along with the knee- 

 joint and skin of the leg." In order to lead off the skin current 

 the prepared flap must be carefully spread out on a clay block, 

 one electrode being in contact with this latter, the other with the 

 centre of the exterior skin surface. Hermann's modification (75), 

 as described above, is yet more convenient and sparing of injury ; 

 the whole frog is used, curarised to immobility, when the current 

 can be led off' with circulation intact after freeing the pelvic 

 portion of both sciatics (from the back) either from symmetrical 

 points of both skinned legs, or, as is perhaps better, from some 

 point of the skin of the leg, and the exposed, undisturbed surface 

 of the thigh muscles on the same side. In the latter case the 

 whole skin current comes into play, and must, as a rule, be com- 

 pensated beforehand. 



In Eoeber's experiment it was found that where the entering 

 skin current was of any considerable proportions, excitation of 

 the nerve invariably produced a greater or less diminution of 

 E.M.F., and " as this occurs in a preponderating majority of 

 cases," Eoeber does not consider " this ' negative variation ' 

 of the gland current to be, generally speaking, the consequence 

 of excitation of the gland nerves. With an originally low magni- 

 tude of current, on the contrary, there is sometimes increase 

 instead of decrease, a positive instead of a negative variation." 

 Engelmann also found in the same object an almost invariable 



