v ELECTROMOTIVE ACTION OF EPITHELIAL AND GLAND CELLS 485 



of its E.M.F. This is best examined in preparations where 

 normal electromotive activity has previously been altered in 

 various degrees by treatment with dehydrating salt solutions. It 

 is then found without exception that the negative variation is less 

 on direct excitation of the lingual mucosa, in proportion with the 

 weakness of the entering current. Soon, however, another phenn-. 

 menon makes its appearance in the gradual development of a 

 positive fore-swing and positive after-effect, which, as it were, 

 enclose the negative variation. Sometimes the latter is wholly 

 wanting, and even with strong excitation there will be only a 

 monophasic, positive deflection, often of considerable dimensions. 

 This only occurs, however, at a very advanced stage of dehydration. 

 Having in view the facts communicated above, which refer 

 exclusively to the results of direct excitation of the lingual 

 mucosa, we may curtail the discussion of the following, i.e. the 

 appearances due to indirect excitation from the nerve, since in all 

 essential points they coincide with the former. Hermann and 

 Luchsinger (79), examining into the "secretion currents" of the 

 frog's tongue when led off from two symmetrical points on the 

 mucosa with excitation of the glossopharyngeal or hypoglossal 

 nerve, express the " perfectly regular " result of their experiments 

 as follows : " After a visible latent period, the excitation of a 

 glossopharyngeal nerve produces a current in the excited mucosa, 

 ingoing at first, but which immediately gives way to an outgoing 

 direction, after which there is once more, whether the excitation 

 is over or in progress, a powerful incoming current that long 

 outlasts the excitation (where this is not continued), reaching its 

 maximum slowly, and then disappearing again with extreme 

 reluctance." This effect will be seen to agree, generally speaking, 

 with the results of direct excitation experiments, apart from the 

 positive fore-swing and (in our observations far less strongly 

 marked) positive after-effect of the second negative phase, which 

 we have only observed, in the manner described by Hermann, in 

 preparations where the normal electromotive activity is already 

 considerably weakened. Our own experiments relate throughout 

 to specimens of R. temporaries kept over winter during the months 

 of January and February. We held it advisable with regard to 

 the comparison possible between the series of experiments described 

 above, and those to be discussed in the sequel, to continue leading 

 off from the upper and lower surface of the tongue, with com- 



