. Essentials of medical electricity . 3. If using an incandescent current, never bring the metallicpart of the cords or electrodes together unless the crank is wellover to the right. 4. Prevent all dust from settling on the class plate. 5. Renew the graphite covering on the glass plate as oftenas marks of wear are visible by rubbing graphite over the cir-cumscribed area from a very snft pencil. This instrument is chiefly valuable in enabling us to use anincandescent-electric light current for all strengths of medico-galvanic needs. Water Rheostat.—This is an arrangement by which the elec-trica
. Essentials of medical electricity . 3. If using an incandescent current, never bring the metallicpart of the cords or electrodes together unless the crank is wellover to the right. 4. Prevent all dust from settling on the class plate. 5. Renew the graphite covering on the glass plate as oftenas marks of wear are visible by rubbing graphite over the cir-cumscribed area from a very snft pencil. This instrument is chiefly valuable in enabling us to use anincandescent-electric light current for all strengths of medico-galvanic needs. Water Rheostat.—This is an arrangement by which the elec-trical current is passed through water by means of a movable4 50 ESSENTIALS OF MEDICAL ELECTRICITY. conducting rod ; the stretch of water through which the currentflows is increased or diminished, a long stretch of water, ofcourse, offering greater resistance, and thereby resulting in aweaker current than a short stretch. By inserting or withdraw-ing the rod the current strength may be very gradually in-creased or diminished. Fig. Water Rheostat. The conducting wires from the battery should be located in aconvenient part of the apartment, and the current controllerattached thereto; from the controller the current should pass tothe milliampere meter, and thence to the object of treatment. Several objections may be noted as applying to the employ*ment of one-fluid cells. FARADISM. 51 1. The acid solution, by its continued action upon the elements,becomes constantly more and more dilute, and as a result evincesa progressive loss of power. 2. As the solution increases in dilution the internal resistanceof the cell also increases, a saline or acid solution being a betterconductor than pure water. 3. The action of the solution upon the positive plate resultsin an accumulation of deposit in some instances ; thus, wheresulphuric acid, zinc and copper are used, zinc is gradually de-posited upon the copper plate, resulting in impairment ofcurrent strength, i. c, the potential of the co
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