CHAPTEE V 



ELECTROMOTIVE ACTION OF EPITHELIAL AND GLAND CELLS 



EVEN in the muscle it is not possible to make any sharp 

 separation between " current of rest " and " current of action," 

 seeing that both manifestations are to a certain extent distinct 

 in degree only, and still less can this be effected with regard 

 to the electromotive action of other animal and plant cells, in 

 which differences of potential (irrespective of whether they 

 appear before or during artificial excitation, and are relatively 

 altered in one or the other direction) are always and solely the 

 expression of chemical dissimilarity in adjacent parts of the living 

 continuum. From this point of view therefore it is purely arbi- 

 trary, and indeed illegitimate, to speak of the " rest current " 

 of a glandular, mucous membrane, or vegetable cell-aggregate, in 

 contradistinction to the current of action, since in both cases 

 we have a reaction deriving from the same cause, i.e. the 

 presence of certain chemical processes of metabolism at given 

 points of the mass of protoplasm, which are only altered 

 quantitatively or qualitatively, by direct or indirect excitation. 

 This does not of course exclude the event that with initial 

 absence of current in such parts, differences of potential may be 

 first called out, as in " parelectronomic " muscle, by excitation. 



It is therefore advisable to treat the electromotive reactions 

 of glandular and epithelial cells together, without separating 

 the discussion of the effects which appear during rest and 

 during action, as was convenient in muscle. It is perhaps 

 a consequence of the difficulties which the long -pre vail- 

 ing molecular theory threw in the way of any systematic 

 account of the facts under consideration, that the experimental 

 treatment of this part of the field is quite disproportionate to 



