Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

esting to know exactly what becomes of the native normal or abnormal nerve current, in health and in disease, at the lime •when that given nerve is called upon to render to the muscles or to the nervous centres, those modifications that we recognize and manifest in sensation or motion. This, for a motor nerve, we conclude, is that which produces a degree of vibrating ten- sion or tetanus of a greater or less degree in the depending muscle or muscle group ; while, for the nerves of sensation, it is that which produces the most life-like sensations. These are best imitated and observed from the effects of induction currents of galvanic electricity. But first let tis observe the result of the influence of a constant voltaic current over the native animal, muscular, and nervous current. If we cause a feeble but steady battery current to travel in the same direction with the native nervous current, as through an isolated nerve, we immediately see that the latter is increased; while if the direction of the two currents are opposed, — the artificial to the natural, — then the native intensity is found di- minished. Either of these conditions can be thus maintained as long as the projecting portion of living nerve experimented upon is traversed by the gentle, steady voltaic stream to certain lim- its ; but they cease immediately when the latter current is removed. It is thus determined that by means of the circulation of a foreign current through the trunk of a nerve, there is brought about an alteration in the entire nerve, even with its extended branches included. This alteration M. Dubois-Reymond calls the electro-tonic state of the nerves. It is also called electro- tonus. He gives two forms or phases of this induced state of the nerves: the one is where the original nervous current re- ceives an augmented intensity, which he calls the positive; and the other is where the nerve suffers diminution of the native nerve current, and this he calls the negative. From the study of these phenomena, we may explain by sup- posing that the electro-tonic state which the nerve is caused to assume is due to the molecular polarization of the nerve, analo- gous to that which is always determined in all conducting bodies