A manual of practical medical electricity - the Röntgen rays and Finsen light (1902) (14597014028)

Identifier: manualofpractica00turn (find matches)

Title: A manual of practical medical electricity : the Röntgen rays and Finsen light

Year: 1902 (1900s)

Authors: Turner, Dawson

Subjects: X-Rays Electrophysiology Electrosurgery Electric Stimulation Therapy Electrotherapeutics X-rays Electrophysiology Electrosurgery

Publisher: New York : William Wood & Company

Contributing Library: Francis A. Countway Library of Medicine

Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

Text Appearing Before Image:

acertain galvanometric deviation, and then, having with-drawn the body, to interpose in the circuit in its steadsufficient known resistance by means of a rheostat, or setof resistance coils, to produce exactly the same galvano-metric deviation ; then the known resistances you haveinterposed must be equal to the unknown resistance of thepart of the body you have tested. The most accuratemeans of measuring resistances is with a Wheatstonesbridge and a set of standard resistance coils, and in the caseof an electrolyte, such as the body, the alternating current Resistance 65 and a telephone. The latter is Kohlrauschs method(Fig. 30). Polarization is thus obviated ; the directionof the current is reversed too rapidly to allow of anysensible electrolysis. It is not believed that accuratemeasurements of the resistance of electrolytes can be madeby the continuous current. Rheostats, or instruments for interposing resistance, areof various kinds. A convenient form will be mentionedfurther on.

Text Appearing After Image:

Fig. 30.—Kohlrauschs Bridge. To sum up our remarks upon resistance in regard togalvanization : The resistance of the body depends mainlyupon : 1. The condition (moist or dry) and thickness, presenceof hair follicles and sweat glands, of the skin. 2. The size of the electrodes. 3. Firmness of surface contact. 4. Length of application. 5. Distance apart of electrodes.* 6. Temperature of the skin. * This consideration is practically nullified by the overwhelminginfluence of the first two. 5 CHAPTER VI CURRENT-STRENGTH This represents the quantity of electricity which flowsalong a given section of the circuit in a unit of time, andthe medical unit of current-strength we term the milh-ampere. Let us return to the water analogy. The difference oflevel or of head in two connected cisterns corresponds todifference of potential or E. M. F.; the size of the streamalong the connecting-pipe to the current-strength. If thecisterns be connected by a large and short pipe (thick andshort copper wir

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1902

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