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

less extent of the trunk of that nerve. For instance: if we test the nerve viedianvs, it is sufficient to embrace between the electrodes only that portion of this nerve that lies along the bor- der of the lower third of the muscle biceps; but the facility of the nerve excitement and the resulting contraction, increases with the length of the nerve extent that is included between the poles. 3. A tonic contraction can he produced by directing a weaker, steady, and continuous current of electricity through a nerve trunk, even in cases where, if the same stream is applied in a similar manner but directly over the muscles of that same limb, it is not able to produce even an opening convulsion. 4. A current can cause insufferable pain without a tonic contraction being produced ; while in another person, or even in the same person at another time, that same current produces strong tonic contractions, and scarcely any pain. 5. The production of the tonic contraction is, however, gener- ally facilitated by the same conditions which also make the " closing convulsions" lighter ; and that is, by a sudden letting on of the current. But there are also cases where only after a moderate and partial removal of the electrode from over the nerve trunk, where it has been applied for the minute before, the tonic contraction commences in the reach of that nerve, and lasts as long as the electrode is thus lightly touching the skin with a moist contact. 6. From twenty to thirty of Daniell's elements are usually sufficient to produce a visible tonic contraction on the arm of a well man. But there are persons who require even double that number to show this phenomenon. When a tonic con- traction is not produced at the first application of the elec- trodes, it usually appears on the second application ; i. e., after the first application has been retained, and thus allowed one minute, or so, of in-working to quicken the nerve sensibility. This occurs in those cases where the current obtains only the lighter " entrance convulsions " when applied directly to the muscles. 7. Most young people, and all who have strong muscles,