v ELECTROMOTIVE ACTION OF EPITHELIAL AND GLAND CELLS 473 



off so much water from the watery tissues of the tongue, that 

 they appear visibly shrunken and darker in colour than under 

 normal conditions. In this state the entering current of the 

 inucosa is always very weak or wholly wanting-. 



These last appearances lead directly to the consideration of 

 the mode of action of other substances which produce chemical 

 metabolism in the living cell. In the first place there are the 

 two gases which play such an important part in the vital processes 

 of the organism, oxygen and carbon dioxide, whose special signi- 

 ficance for certain electromotive reactions of plants and animals 

 is well established. Engelmann showed that on driving out 

 oxygen by an indifferent gas (N or H) the E.M.F. of the skin 

 current sinks gradually, increasing again quickly so soon as 

 atmospheric air is reintroduced, until the initial height is not 

 only reached, but even exceeded. C0 , on the other hand, pro- 

 duces an extremely rapid fall of E.M.F., which is only arrested 

 when the surrounding atmosphere contains a low percentage of 

 the gas. A similar effect of want of has been recently 

 demonstrated in plant currents by Haacke (Flora, 1892, Heft 

 iv.) We can attest a similar effect of these two gases upon the 

 frog's tongue. The method of experiment was essentially based 

 upon that of Engelmann ; the preparation (lower jaw and tongue 

 lying on a block of salt clay) was placed with the leading-off 

 electrodes in a gas-chamber, consisting of a glass vessel, with four 

 tubes, through which the gases could be led into the chamber. 

 The E.M.F. of the incoming lingual current invariably fell on 

 driving out 0, as well as on introducing C0 9 , in the first 

 case rather slowly, in the second, on the contrary, very rapidly. 

 This simple contrivance may also be employed for testing ances- 

 tlicfics (ether, chloroform) : even a small quantity of these sub- 

 stances in the form of vapour produces a considerable diminution 

 of E.M.F. in the entering current, which, if the action does not 

 last too long, is restored by driving pure air through the 

 chamber. 



The mucosa of the throat and cloaca of the frog give precisely 

 similar relations. Engelmann (77) had previously demonstrated 

 electromotive effects in both these preparations. Again, in both 

 cases, we have, under normal conditions, an " entering " current, 

 often of considerable E.M.F., and hardly below that of the lingual 

 current. Yet the histological structure is widely different. Both 



