v ELECTROMOTIVE ACTION OF EPITHELIAL AND GLAND CELLS 481 



inent, since the nerves that supply its glands can be exposed 

 without difficulty. 



We have seen the extent to which the strength of the normal 

 entering " tongue current " is affected by the least disturbance to 

 the surface of the mucosa. In nearly every case it increases 

 rapidly after contact with the point of the leading-off electrode, 

 both in the excised tongue and in the preparation in situ. 

 That this is merely due to the decline of a negative variation 

 (produced by contact of the mechanical stimulus) in the current 

 of rest follows from the fact that, on closing the galvanometer 

 circuit, the slightest movement of the electrode point on the 

 surface of the tongue, or gentle rubbing of the spot led off, 

 at once produces a rapid fall of E.M.F., which usually occurs 

 the more vigorously in proportion with the strength of the 

 maximal rest current. This negative variation declines very 

 rapidly, and may often be reproduced if the excitation is repeated. 

 Experiments to determine the magnitude of excitation required, 

 show that extremely slight impacts are needed under favourable 

 conditions. Stroking with the point of a hair, or the fall of a 

 drop of salt solution, nearly always produces a marked variation. 

 With stronger excitation distributed over a larger area, the effect 

 is increased, and a current of rest that is not too strong may 

 easily be reversed under these conditions, especially if (c.y. 

 through moderate cooling) there is an a priori tendency in that 

 direction. If kept at a low temperature in a little water, weakly 

 curarised, R. temporaries will often exhibit a reversed (outgoing) 

 rest current of considerable dimensions, if the leading-off elec- 

 trodes are placed, one on the surface of the tongue, the other on 

 the exposed muscles of the leg, directly after the lower jaw has 

 been drawn back by a thread previously passed through it. 

 This outgoing current, which must certainly be referred in part 

 to cooling, is often as strong as the normal entering current, but 

 diminishes rapidly if the electrodes are left undisturbed, and finally 

 becomes reversed, i.e. normal. During the whole of this period 

 the slightest friction with the tip of the electrode in contact 

 with the tongue will at once produce a swing back of the 

 magnet, in the direction of increase of the outgoing, or diminution 

 of the incoming, current, followed again by a prompt reversal. 

 In such cases the reversed current immediately after the throat 

 has been opened is doubtless only partially due to the previous 



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