242 STUDIES IN ELECTRO-PHYSIOLOGY: 



For electro- diagnosis, however, a shunt is unnecessary, 

 and as the resistance of the coil of a d'Arsonval galvano- 

 meter seldom exceeds 2,000 ohms, it should not be used 

 with that type of recording instrument at all. If, however, 

 it is desired to do so, a " universal " shunt is recommended. 

 It is a golden rule to " limit the apparatus." To avoid 

 leakage is to avoid trouble. Let the top of the testing- 

 table be of teak or other hard wood, and paraffin-wax it. 

 Also have a gas-fire or electric radiator in the testing-room 

 and maintain a standard temperature. 



CONNECTING WIRES. 



To connect the galvanometer with the short-circuit key 

 and electrodes use the best electric light flex (30 to 40), 

 untwisting same so as to have single wires. 



EARTH CONNECTION. 



Thick (preferably insulated) copper wire soldered to 

 the water-main and the other end brought and connected 

 to a copper rod or tube in the testing-room, makes a very 

 good " earth." 



THE ELECTRODES. 



These are seven in number, and are made for me by 

 Messrs. Hodges & Co., of St. John Street, Clerkenwell. 

 For the hand-to-hand deflection I use solid German silver 



Fig. 184. 



rods (heavily silver-plated), 5 \ in. by f in., provided with 

 a thumb-piece and a terminal at the upper end (Fig. 134), 

 the thumb-pieces being shaped as Fig. 135 in plan. 



