Handbook of electrotherapeutics Author:Unknown Author Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: LECTURE II. Accessory Apparatus : Selector or Element Numerator—Polarity Changer—Galvanometer—Measurement of the Absolute Strength of the Current—Rheostat—Con... more »ducting Wires—Electrodes and their Various Forms—Electrical Table.—Physical and Physiological Recognition of the Poles. The proper practical application of the apparatus above described requires a number of accessory apparatus, upon the proper construction of which depends in good part the ease and exactness of the application of the current for diagnostic and therapeutic purposes. Under the term selector, or better, element numerator (according to Zech) is meant a small apparatus which should not be absent in any galvanic battery and which enables us to include or exclude from the circuit any number of elements desired—if possible without interruption of the closed current. This is effected by a number of contacts corresponding to the number of elements, and which may be connected with the conducting wires by the most various methods ; either by means of contact springs which are fixed to a sliding movement, to be moved to and fro (Stohrer), or to a revolving disc, and are so arranged that the last contact is not broken until the next has been reached ; or by means of two plugs, one of which is not removed until the other has already been placed in the next. The most perfect selector is that which enables us to include one additional element at a time in the circuit; this is frequently only possible for the smaller number of elements, for the larger ones each three, five, or ten elements. A very important accessory apparatus, which is indispensable for all more exact investigations, is the polarity changer. This little apparatus is introduced into the circuit for the purpose of changing the direction of the curre...« less