The chemical action of a continuous Voltaic current is sometimes useful in the removal or dispersal of tumours, and in the consolidation of aneurisms, one or more needles being introduced into the tumour, and connected with a Voltaic battery. I shall discuss this subject in our next Lecture, but I have here some of the most generally useful needles (Fig. 16), and I have had made for them holders with eyelet-holes for the attachment of conducting wires which render the operator independent of special conducting cords, for with a coil of insulated wire and a pocket knife he can fit up his needles in a few minutes in any way best adapted to his proposed operation. [Illustration: FIG. 16. Electrolysis Needles and Needle-holders. By pressing the spring side B, the holder opens as shown in C, to grasp the needle D. The wire is twisted into the eyelet hole-A.] [SN: Precautions in mode of Application.] Having now considered the more generally useful methods of application, it may perhaps not be out of place to remind you in concluding this part of our subject that certain precautions are necessary to be observed. We must keep constantly before our attention that we are prescribing or administering an exceedingly powerful remedy, and with all new patients we should commence with a minimum dose, watch its effect, and if we need to increase it, do so gradually--_e.g._, muscular contraction being sought we must use the power just sufficient to produce it and _no more_--and so on with other applications; and it is especially necessary to use care in applying the Voltaic current to the face, neck, or any part of the head. Duchenne blinded a patient by suddenly applying a current from 40 cells to the facial muscles, and he had the candour to publish his misfortune. Sudden applications and sudden cessations should especially be guarded against. The cessation shock can, of course, only occur in cases where the conductors having been held immovable, and the current gradually increased, one or both of them has been abruptly, and it may be inadvertently, removed; and I have known a patient so frightened by such a cessation shock as to decline further treatment. The negative pole of a Voltaic battery will, if frequently applied to the same spot, soon cause a sore, and to avoid this the point of application should be slightly varied occasionally; and let me impress upon you, Gentlemen, the importance of always testing electricity upon yourselves before applying it to a patient. Use as many galvanometers, or so-called “instruments of precision,” as you like, but use in addition the back of your left hand as a convenient approximate test for the Voltaic, and your thumb muscles for the Faradaic current, except when about to apply electricity to your patient’s head or face, and make it then an invariable rule to first apply to your own face the same strength of current you are about to administer to your patient’s. If you