v ELECTROMOTIVE ACTION OF EPITHELIAL AND GLAND CELLS 475 



Under these conditions the entering current is much stronger 

 than in the separated membrane, and the only doubt can bo 

 whether electromotive action of other parts (injured muscles, 

 etc.) may not be involved in it. Such interference can easily be 

 excluded if the same preparation is examined, as before, after 

 destruction of the surface epithelium, or the entire removal of the 

 ciliated mucosa. We have never then observed any marked 

 differences of potential, so that this objection must be regarded as 

 unfounded. The mucous coat of the cloaca is usually examined 

 by slitting the cloaca longitudinally as cautiously as possible, and 

 spreading it out on a clay block without actually touching the 

 mucous surface, which can then be led off as usual. 



Up to a certain point the mere look of the membrane will 

 show in the one case, as in the other, whether it will yield a 

 strong or weak current. If the mucosa of the throat (as is usual 

 in winter) looks transparently pink and moist, and if the cloaca 

 is filled with soft or liquid matter, a strong current may be 

 reckoned on with tolerable certainty ; but if, on the contrary (as 

 is usual in summer with frogs that have been in hand a long- 

 time), the ciliated mucosa is dim and pale, or the cloaca contains 

 only a few hard excreta, the entering current, although generally 

 present, will be extremely feeble. This seems a direct indication 

 that the secretory activity stands in both cases in immediate and 

 close relation to the electromotive action of the mucous membrane. 

 To this it must be added that the ciliary movement often 

 occurs normally, as far as may be judged from the onward move- 

 ment of blood platelets or similar bodies, while the entering 

 current is quite, or almost, wanting ; and we have, on the other 

 hand, though more rarely, observed cases in which, notwithstand- 

 ing a weak ciliary motion, the E.M.F. of the current was unusually 

 high. The mucosa in this case was invariably covered with 

 a tolerably thick layer of slimy secretion. It would appear 

 that the mechanical injuries associated with exposure and 

 extension have a much less pernicious effect upon the ciliary 

 movements of the mucosa of the throat than upon its electro- 

 motive action. We have frequently observed in these prepara- 

 tions that the ciliary motion continues for hours with the utmost 

 vivacity, while minimal deflections alone indicate the presence of 

 a weak entering current. The effects of pilocarpin poisoning may 

 also be quoted in favour of the view here advanced, which regards 



