vii.] IMPORTATION OF IONS 125 



with shifting contacts. We all know how difficult it is to pre- 

 serve a limb absolutely quiet, and that even when we think that 

 our muscles are completely at rest, a "thought-reader" can 

 obtain information from our unconscious movements. It is no 

 easy matter to have a loose pad immobile against the skin, and 

 if it be fixed by a band, the least swelling or movement will alter 

 its pressure against the skin ; and I cannot say that I have suc- 

 ceeded in satisfying myself that the irregular deflections that 

 certainly do occur with a subject keeping as quiet as possible, 

 and more markedly when the subject is anywise startled or 

 stimulated, have been anything else than the effects of accidents 

 of surface contact. I am willing to admit that they might be 

 accidents of nervous tension giving true alterations of skin- 

 currents, but I cannot admit that this possibility has been 

 proved to the exclusion of the coarser fallacy. Will any one 

 undertake to clear up this point? If so, perhaps it may be 

 worth while to mention that the skin can be locally atropinised * 

 by means of a belladonna plaster, and that obviously a locally 

 atropinised skin should show no effect of glandular action, but 

 the usual effects of accidents of contact. 



I do not think that these observations on the human sub- 

 ject are particularly satisfactory, and shall not dwell upon them 

 any longer. I will use the remainder of the hour to place 

 before you certain facts relating to the transport of medica- 

 ments into the human body under the influence of the galvanic 

 current. 



74. Importation of ions. All such facts are illustrations of 

 the principles of electrolytic conduction. If a sufficiently strong 

 current is passed through a saline solution, or, as I am about to 

 show you, through a porous electrode soaked in a saline solution, 

 the electro-positive kations of the salt travel with the current 

 from the anode to the kathode, while the electro-negative 

 an ions travel against the current from the kathode to the anode. 

 Taking, e.g., the case of NaCl, the Na travels with the current, 

 the Cl against the current. You may for the present purpose 



* Aubert, "Sweat-prints," Ann. de Dermatologie, 1877-8; Article 

 " Sueur," (by Frangois Franc) in Diet. Encycl. des Sciences Medicales, xiii. 



