474 ELECTRO-PHYSIOLOGY CHAP. 



in throat and cloaca the mucous coat is " glandless " in the 

 ordinary acceptance of the word, there being in both cases only 

 a single layer of cylindrical epithelium, consisting in the throat 

 of ciliated cells with goblet cells interspersed between them, in 

 the cloaca almost exclusively of the latter. Multicellular glands 

 are entirely wanting. From these very reasons the preparations 

 afford much more obvious and simple conditions of leading-off 

 than the lingual mucosa, so that certain objections to which the 

 latter is fairly liable drop out of court without prejudice. Since 

 in the cloacal mucosa ciliated cells are altogether wanting, while 

 its electromotive action corresponds in every respect, on the one 

 hand with that of the ciliated mucosa of the throat, on the other 

 with the sparsely ciliated lingual mucosa, we cannot but conclude 

 that in all three cases the true electromotive elements are the mucous 

 cells, whether present as elements of compound glands, or as goblet 

 cells. But it was necessary to test this view, inasmuch as Engel- 

 mann held the ciliated cells themselves to be the active electro- 

 motive elements, and was inclined to derive the throat current 

 from them. Hermann, too, indicated as a possibility that the 

 ciliary movement might be regarded " from the point of view of 

 an (' irritative ') alteration occurring in the external cell-layers." 

 Our own observations do not, however, bear out this suggestion. 



The method of investigation both in throat and cloaca was 

 extremely simple. Engelmann, as a rule, separated out the 

 mucosa from the layers beneath it, and led off from the inner 

 and outer surfaces of the membrane stretched over a cork. 

 But even with the greatest precautions this entails some 

 mechanical injury, and since as we have frequently experienced 

 the intensity of electromotive action in the mucosa is affected 

 to an extraordinary degree by even the slightest stretching 

 or tearing, it is preferable to lead off from the mucosa in 

 situ. For this it is only necessary to remove the outer skin 

 of the head as far as the wall of the upper jaw, so as to avoid 

 any accidental interference from its electromotive properties, and 

 then to cut out the whole upper jaw by as deep a section as 

 possible. This is placed in a watch-glass in a little 0'5 

 salt solution, with the mucous surface uppermost, after which it 

 is only necessary to dip one brush-electrode into the latter, while 

 the point of the other is in contact with any point of the mucous 

 surface, in order to lead off with as little disturbance as possible. 



