Lectures on nervous diseases from the standpoint of cerebral and spinal localization, and the later methods employed in the diagnosis and treatment of these affections . the needle,Avhereas in most instruments of thebetter class the oscillations of theneedle average at least twenty-fivebefore it comes to rest. In this in-strument the vibrations seldom ex-ceed from five to six. Shunts are pro-vided in order to measure very highcurrents. I regard this instrumentas fully equal, if not superior, toHirschmanns expensive instrument. The Eheostat. — This is anappliance to regulate the externalresista
Lectures on nervous diseases from the standpoint of cerebral and spinal localization, and the later methods employed in the diagnosis and treatment of these affections . the needle,Avhereas in most instruments of thebetter class the oscillations of theneedle average at least twenty-fivebefore it comes to rest. In this in-strument the vibrations seldom ex-ceed from five to six. Shunts are pro-vided in order to measure very highcurrents. I regard this instrumentas fully equal, if not superior, toHirschmanns expensive instrument. The Eheostat. — This is anappliance to regulate the externalresistance of a battery under varyingcircumstances. Several devices aremade for this purpose, but the fluidrheostat (containing water, solutions of salt, solutions of zinc sulphate, etc.) is often all that is requiredfor medical uses. It is cheap, easily managed, and modifies the current-strength. It is liable to polarize f Avhen used too long, and does not actso well with strong curi-ents as with weak ones. It consists of a glasstube filled with water or some prepnred solution (preferably a forty percent, solution of sulphate of zinc), through which a brass rod or an. Fig IA.—A Fluid Rheostat.—This instrumentis used to throw additional external resistanceinto circuit. Coil rheostats are more reliable,because fluid is decomposed and causes polari-zation of the metal points when strong currentsare used. Some of the graphite rheostats arepreferable to many containing fluid, and arecheaply made. * This is shown in a cut of my own cabinet battery, on a succeeding page, and inFig. t We speak of an element as polari?.cd^ when bubbles of hydrogen or oxygen accu-mulate upon it, and thus diminish its efficiency. 632 LECTURES ON NERVOUS DISEASES. amalgamated zinc electrode is made to slide \\\) and down, thus separatingits lower end from a button at the bottom of the tube. When the cur-rent is sent through this rod, it is forced to pass through the depth offluid that lies below it i
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