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A MANUAL OF PHYSIOLOGY 



electro-cardiographic curves* (Fig. 283), which express the actual 

 changes in the potential difference between the two points led off. 

 They distinguished in every one of these constructed electro-cardio- 

 grams five points or cusps, three of which indicate relative negativity 

 of the base of the heart to the apex, and two negativity of the apex to 

 the base. The capillary electrometer has now been largely superseded 

 by the string galvanometer (p. 619) for the investigation of the human 

 electro-cardiogram (Figs. 284-287) . Records are obtained by magnify- 

 ing and photographing the mo vemen ts of the q uart z fibre . The electro- 

 cardiograms are distinctly affected by exercise and by the position 







FIG. 282. ELECTRO-CARDIOGRAMS FROM MAN 

 (CAPILLARY ELECTROMETER), (EINTHOVEN 

 AND LINT). 



The image of the capillary magnified eight 

 hundred times was projected on a moving photo- 

 graphic plate. The figure is a reproduction of 

 the record (reduced to two-thirds of its original 

 size) obtained from the same individual at rest 

 (upper curve), and immediately after vigorous 

 muscular exercise (lower curve). The move- 

 ments of a tuning-fork, making fifty complete 

 vibrations a second, are shown below the cardio- 

 grams. The sulphuric acid pole of the electro 

 meter was connected with the thoracic wall in 

 the neighbourhood of the apex of the heart, 

 and the mercury with the right arm. The 

 elevations A, C, D, indicate negativity of base 

 to apex ; the notches B and Cj_, negativity of apex 

 to base. 



FIG. 283. - CONSTRUCTED 

 ELECTRO - CARDIOGRAMS 



FROM MAN (ElNTHOVEN 



AND LINT). 



The curves are constructed 

 from the photographic records 

 shown in Fig. 282. These and 

 not the photographs are the 

 true expression of the actua 

 changes of potential during 

 the cardiac cycle. Time is 

 laid off along the horizontal, 

 and electromotive force along 

 the vertical axis, the same 

 space being allotted to ten 

 millivolts (i.e., T 5 volt) as 

 to one second. 



of the body, and very markedly in disease. They are being more 

 and more employed in clinical investigations. The galvanometer 

 may be connected with the two hands, or better, with the right hand 

 and the left foot. The two feet are the most unfavourable com- 

 bination. 



Central Nervous System. It was discovered by du Bois-Reymond 

 that the spinal cord, like a nerve, shows a current of rest between 



* In all accurate work with the capillary electrometer such curves must 

 be obtained by construction from the direct photographic records, which 

 do not themselves give an absolutely true picture of the variations. 



