Identifier: physiologybioche00macl (find matches)
Title: Physiology and biochemistry in modern medicine
Year: 1918 (1910s)
Authors: Macleod, John James Rickard, 1876-1935 Pearce, R. G. (Roy Gentry), 1884-
Subjects: Physiology Biochemistry
Publisher: St. Louis : Mosby
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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oducing into the circuit in the opposite direction the re- *A certain amount of repetition of matter previously discussed has been found advisable in thesechapters for which the indulgence of the reader is requested. tit is really unnecessary to use the so-called nonpolarizable electrodes. Glass vessels containing20 per cent NaCl solution with the zinc plates dipping into them are quite satisfactory. 259 260 THE CIRCULATION OF TIIK BLOOD quired amount of current, called the compensating current, to bring thestrong shadow hack to the zero or midposition. In order that the rec-ord obtained may he quantitative in character, it is further necessarythat the movement of the string he standardized. This is done by as-certaining to what extent the string moves when a current of knownvoltage is sent through it and by altering the tension of the string so thatone millivolt of current causes an exclusion of one centimeter of thestring shadow on the photographic plate. It would take us beyond the
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Eig. 81.—Electrocardiographic apparatus as made by the Cambridge Scientific Materials Co. Con-tact electrodes are shown, but the immersion electrodes described in the context are preferable. confines of this volume to go in any greater detail into the technic in-volved in taking electrocardiograms, but it may be said that this is byno means difficult, provided the instructions which are supplied withthe instrument are carefully followed. In practice the taking of elec-trocardiograms is indeed quite a simple matter, and the extremely im-portant information which they give us concerning the mechanism ofthe heartbeat and the evidence of myocardial disease should make theiremployment a universal practice in all cardiac clinics. Some of theseclinical applications arc described elsewhere (page 266). ELECTROCARDIOGRAMS 261 What particularly interests us here is the contour of the electrocardio-gram in n normal person (Fig. 82). It will be observed thai there arethree waves above the Line o

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