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

these sensations. Indeed, if it should be still longer continued, and a still stronger current be employed, there could be pro- duced a sensation of numbness, and perhaps of coldness, which remains a few minutes after the current is removed. Then the physiological sensations soon return again, however, with a some- what increase of function. If electro-magnetic currents are thus brought to bear upon these nerves through the skin, then sensations are produced which vary according to the intensity of the current, the rapidity with which it intermits, and the sensitiveness of the skin. The sensations are different, also, on different parts of the body and limbs. They may be extremely pleasant, or as extremely disagreeable, or even intolerably painful; or there may be a together-drawing, contracting, pinching, pursing, prickling, or, as sometimes experienced, a burning sensation. These cease when the current is opened. An induction c\irrent of the same quantity and intensity has a greater effect upon the sentient nerves, in proportion to the frequency of the interruptions of the current, up to a certain degree, which, for instance, may be about all the nerves can bear; but if the vibrator is screwed up a trifle, so as to make the interruptions extremely fine and rapid, then the current is more easily borne, and not only so, but it then becomes almost or quite pleasant, particularly if it is being applied to the back or shoulders. But I believe there is in this case more indirect effect; i. e., reflex action, because this cur- rent more nearly resembles the continuous galvanic current. A pretty rapidly interrupted current has more effect on the sentient nerves than very slowly interrupted currents, because it is the law of their action to feel or retain the effects of an impression for some little but appreciable time, after being acted upon. So where a sentient nerve, that is in health, is subjected to the action of a single blow of an induction current, if of low tension, there is almost no sensation ; but if these blows or shocks are then repeated faster and faster, the sensations will likewise increase, because the sentient nerve is not now in its normal state, i. e., when it receives the second, and third, and succeeding shocks, but is in an excited condition, or polarized. Thus it is easy to