60 



EXPERIMENTAL PHYSIOLOGY 



is deflected to one side or the other to an extent varying with the E.M.F. the 

 tension of the thread being supposed constant. The movement is observed with 



a microscope, or the magnified image of 

 the thread is photographed on a moving 

 sensitised surface. The method of con- 

 ducting the experiment is very similar 

 to that employed for the capillary 

 electrometer. For certain investigations, 

 especially those relating to the electrical 

 conditions accompanying the action of 

 the heart, the string galvanometer is 

 more convenient than either the capil- 

 lary electrometer or the needle galvano- 

 meter. It has been largely adopted by 

 clinicians, since the heart-records ob- 

 tained by it (electro-cardiograms) furnish 

 valuable indications as to the nature of 

 cardiac affections which might be other- 

 wise difficult to diagnose. When used 

 for the human subject the two hands, 

 or one hand and an opposite foot, are 

 placed in vessels of salt solution, and 

 these are connected, by wires, with the ends of the quartz thread. 



Reflecting needle galvanometer. Reflecting galvanometers of high resistance 



k 



FIG. 53. DIAGRAM OP EINTHOVEN STKTNO 

 GALVANOMETER, s, s', SILVERED QUARTZ 

 THREAD, STRETCHED BETWEEN POWERFUL 

 MAGNETS m, m, WHICH ARE PERFORATED 

 TO ALLOW A MICROSCOPE TO BEAR UPON 

 THE THREAD. 



a 



FIG. 54. DIAGRAM OF ABRANGEMENT OF APPARATUS FOR STUDYING MUSCLE CURRENTS WITH 

 GALVANOMETER, g, GALVANOMETER. THE OTHER LETTERS AS DJ FIG. 52. 



were, until recent years, almost exclusively used for experiments in electro- 

 physiology (fig. 54), but have been largely superseded by the instruments that 

 have just been described. 



