A SUMMARY OF PROCEDURE 27 
bridge, a small inductorium to give an alternating cur- 
rent, a telephone receiver for an indicator and a resist- 
ance box. By suitable wiring, illustrated in Fig. 15, 
p. 73, a single resistance box can be used both for vary- 
ing the primary current and as the known resistance in 
the Kohlrausch determinations. 
The stimulating electrodes must be selected with 
special reference to uniformity of contact. Accurate 
quantitative results cannot be gotten under conditions 
of contact variation. For the direct stimulation of 
muscles I have found platinum needle electrodes most 
satisfactory. A piece of platinum wire 2.5 to 3 cm. 
long, and 0.5 mm. in diameter, pointed somewhat at the 
end with a file, is soldered to a suitable length of very 
fine copper wire (diameter 0.2 mm.). The platinum 
needle is thrust directly into or through the muscle 
tissue; the copper wire, carried to the secondary ter- 
minal, affords the very flexible connection necessary for 
avoiding interference with the free movement of the 
muscle. 
For stimulating nerves the glass-inclosed electrodes 
described by Sherrington * are as reliable as any I know 
of. They answer well either for the stimulation of nerves 
deeply imbedded within the body, or for stimulating the 
nerve of the ordinary nerve-muscle preparation. In the 
use of this form of electrode care must be taken that the 
* Sherrington: Jour, of Physiol., 1909, xxxviii, p. 382. 
