EXPERIMENTAL PHYSIOLOGY 



Dry Batteries. These are of very great convenience in that they 

 are always ready for use, do not give off fumes, and contain no fluid 



to be spilt. One of the most satis- 

 factory of these is the Obach dry 

 battery, manufactured by Siemens. 

 In principle, they are usually modified 

 Leclanche cells. 



THE INDUCTION COIL 



The form of induction coil usually 

 employed by physiologists is Du JBois- 

 Xteymond's sledge inductorium (fig. 6). 

 It consists of a coil, a, of fairly stout 

 insulated copper wire wound on a 

 wooden reel in the centre of which is 

 a core of soft iron wires, c. The number 

 of turns of wire in this, the PRIMARY 

 COIL, varies in different instruments 

 from 200 to 500 or more. The ends of 

 the wire of the primary coil are con- 

 nected to the two binding screws / and h. A second coil of much finer 

 wire is wound round a large wooden bobbin, the whole forming the 

 SECONDARY COIL, b. This is fixed to a wooden foot sliding in a 



Fig. 5. — The Leclanche Battery. 



Fig. 6. — The Induction Coil. (McKkndrick.) 



grooved base, m, and the central cavity in the wooden bobbin is of such 

 a size that the secondary coil may be pushed home so as to completely 

 cover the primary coil a. The terminations of the wire of the second- 

 ary coil are connected to two binding screws, only one of which, n, 



