THE MILL1AMPERE3IETElt: The next instrument which the gynecologist should possess, in order to use electricity intelligently, is a galvanometer, an instrument by means of which the intensity of the current may be measured, so that he may be enabled to estimate accurately the dosage administered to the patient. It was formerly the custom, and is still largely so among gynecologists, to use as a guide the number of cells brought into the circuit, but this is a rough method and inaccurate, seeing that the internal and external resistances vary so markedly. To check our results, therefore, and to know exactly what we are doing, it is essential to include a galvanometer in the circuit. We are speaking now purely of the galvanic current, for the measurement of which alone is the instrument of utility.
The galvanometer is subdivided into milliamperes, the unit of elec trical measurement, and the instrument is, therefore, ordinarily spoken of as a milliamperemeter. For routine purposes, an instrument register ing from forty to fifty milliamperes is sufficient, unless, indeed, it should prove expedient to follow in the footsteps of Apostoli and Engelman, who use intensities as high as two hundred milliamperes and over, as we will note when we speak more in detail of the selection and the strength of the current. Sufficient here the statement that, except where electrol
ysis is aimed at, a subject which will be considered in a separate chapter, forty to fifty milliamperes will answer for routine work.
Tn E RH EOSTAT.
A further instrument to which we will refer, although it is not strictly essential to the gynecologist, is the rheostat, which subserves the purpose of interposing resistances in the circuit so as to modify the strength of the current. It is an instrument of greater utility, however, to the neurologist than to the gynecologist, seeing that the latter need not concern himself so much about slight modifications in the intensity of the current. The simplest and most practical form is the water rheostat, which consists in a column of water, interposed in the circuit, "and so arranged that the distances between the extremities of the metals that close the circuit through the water can be increased or diminished at pleasure."'