v ELECTROMOTIVE ACTION OF EPITHELIAL AND GLAND CELLS 497 



The two methods may be combined as follows. The frogs, 

 when well dried, were placed in a large open glass, with a wire 

 cover, the sides and bottom being wrapped in a clean, dry cloth. 

 They were left thus in a warm chamber for at least 24 hours. 

 They were next curarised as slightly as possible to produce 

 immobility, and when paralysed, 12 cc. of 35 / Q salt 

 solution, or better, 0*51 cc. glycerin, were injected into the~ 

 dorsal lymph sac. After two, at most three, hours the dehydra- 

 tion is, as a rule, sufficiently advanced for the experiments to be 

 started. It is unnecessary to enter into all the effects which can 

 be observed on these frogs ; they are sufficiently well known, and 

 have no immediate connection with the facts before us. 



If the electrical activity of the skin of such " dehydrated " 

 frogs is tested as usual, either on single excised portions, or on 

 the entire uninjured animal, the insignificant proportions, or 

 almost complete absence, of the entering current is very striking. 

 This is not merely clue to the greater resistance of the dry skin, 

 for the E.M.F. is slow to recover, even when the led-off parts of 

 the skin are freely moistened with water or dilute salt solution. 

 If an excised portion of the skin, no matter from what part of the 

 body, is now excited directly, or if the freed sciatic is excited by 

 leading off from the external surface of the skin of the leg, and the 

 exposed surface of the muscles of the thigh on the same side, 

 there will under all circumstances be an entering current, i.e. a 

 positive variation of the current of rest, which either makes its 

 appearance alone, or is introduced by a short negative fore-swing. 

 Under these conditions there is never, as before, a mono- 

 phasic negative effect. As regards the strength of the positive 

 effect (always in the direction of an entering rest current), 

 the right degree of dehydration is all-important, and there is a 

 good deal of uncertainty in obtaining this. In favourable cases 

 the positive variation may become as marked as was formerly the 

 strongest negative variation. We have repeatedly seen deflections 

 which drive the scale out of sight when the current of rest has been 

 compensated. But if the latter is still considerable the positive 

 variation grows less and less, and the negative fore -swing is 

 correspondingly greater. Sometimes the entering skin current of 

 the leg, immediately after freeing the sciatic nerve from the 

 pelvis, is extraordinarily marked, notwithstanding the previous 

 dehydration, and this is usually followed by a tolerably rapid 



2 K 



