148 y // 1 'S I O LOG 1C A L Pin 'SICS. [Chap. XV. 



metals, and insert one needle in the muscle to be 

 examined. A deflection of the galvanometer needle is 

 observed. The deflection may be abolished by placing 

 the other needle in oil or other fluid, to which the 

 same temperature as that of the muscle is given, that 

 is, till the needle is brought back to zero. Then, on 

 contraction of the muscle, the slightest change in 

 temperature will cause a deflection, The first current 

 might also be abolished by a compensation current 

 from a Daniell. (See page 121.) Helmholtz' method 

 was to transfix the muscles of the thigh of a frog with 

 one of his needles, formed of six couples, as described, 

 so that the first set of junctions between silver and 

 iron were embedded in one thigh, and the other set in 

 the other thigh. He then waited till the absence of 

 deflection indicated the same temperature in both, and 

 then stimulated one thigh to tetanus. 



CHAPTER XV. 



PHYSIOLOGICAL INDICATIONS FOR THE THERAPEUTICAL 

 APPLICATIONS OF ELECTRICITY. 



THE purpose of this chapter is to give the briefest 

 possible outline of the purposes for which electricity 

 is used in medicine and surgery, and the types of 

 apparatus employed in its production and application. 

 It is hoped that this outline will act as a guide for 

 students and perhaps practitioners, and will aid in 

 the reference to the larger text-books on the subject, 

 a list of the chief of which is given at the end of the 

 chapter. 



Terms in common use. Both the constant 

 current (the current direct from a battery) and the 

 induced current are employed in medicine. By use 



