6 4 



EXPERIMENTAL PHYSIOLOGY 



nified image of the thread is photographed on a moving sensitised 

 surface. The method of conducting the experiment is very similar 

 to that employed for the capillary electrometer. For certain in- 

 vestigations, especially those relating to the electrical conditions 

 accompanying the action of the heart, the string galvanometer is more 

 convenient than either the capillary electrometer or the needle galvano- 

 meter. It has been largely adopted by clinicians, since the heart- 

 records obtained by it (electro-cardiograms) furnish valuable indications 



k 



a 



FIG. 55. Diagram of arrangement of apparatus for studying muscle currents 

 with galvanometer, g, Galvanometer. The other letters as in Fig. 53. 



as to the nature of cardiac affections which might be otherwise difficult 

 to diagnose. When used for the human subject the two hands, or the 

 right hand and left foot, are placed in vessels of salt solution, and these 

 are connected, by a suitable non-polarisable arrangement, with the ends 

 of the quartz thread or wire. 



Reflecting needle galvanometer. Reflecting galvanometers of high 

 resistance were, until recent years, almost exclusively used for experi- 

 ments in electro-physiology (Fig. 55), but have been largely superseded 

 by the instruments that have just been described. 



