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

of fixed electrodes, but merely by wet threads banging from the electrodes, or wire poles, we find tbat tbe closing contraction, and also all tetanus, are avoided. Mark tbat, for it is botb instructive and suggestive. Even when a stronger current is employed does this hold good — an end that M. Matteucci appears to have greatly sought for, as thought by him so desirable for given pur- poses. But the same thing is observed when the solid electrode is not pressed hard against the limb, but is rather held but very lightly to it. Hence we may infer, that a certain pressure of the electrodes over the nerves and muscles is requisite to produce the appreciable varyings in the density of the artificial current, which again produces variations in the native animal electric ' current, and this brings about the increasing degree of muscle contraction. These like trials make it highly probable, therefore, that the galvano-tonic contractions, caused by a constant primary or secondary current, when directed through a nerve trunk, and observed in its depending muscles, belong mostly to those phe- nomena which are produced by variations in the density of the employed current. This explanation, moreover, throws light upon the fact, that a steady and somewhat protracted application of such a current as will cause a closing twitching in the nearest muscle fibres, — that is, in those portions that lie near to the larger nerve twigs, — forms a favorable preliminary to the pro- duction of such a contraction. Now, if the excitability of these fibres or their nerves is not considerable, the fibres remain mo- tionless, i. e., after producing the closing twitch. But, if the ex- citability of these fibres or their nerves is considerably increased, then they'will show, while under the action of the current, a fine and delicate trembling motion, and through this wavy motion of the muscle fibres, prevent the nerves from being affected in an equal measure. The nerve trunk will in that case be conditioned the same as if it were alternately brought near to and removed from the most dense current, without, however, being entirely out of the sphere of its influence ; that is, the different parts of the nerve and muscle fibres will respond to currents of different density, on account of their possessing varying degrees of resist-