62 PHYSIOLOGICAL PHYSICS. [Chap. vii. 



destroyed. A small glass tube drawn to a point at 

 one end is taken. The tube contains two ring-shaped 

 pieces of platinum, fixed a short distance from one 

 another. A fine copper wire from each ring passes 

 through the glass, and terminates in a free end. The 

 tube can be carried on a support attached by a swivel 

 joint to an upright stand. To use it for sending a 

 current to a nerve, tie a piece of thread round one end 

 of the nerve, and by means of the thread pull the 

 nerve gently through the small end of the tube, and 

 lay it over the ring-shaped electrodes. The thread is 

 carried out at the wide end and is held there, and the 

 tube is closed by a small cork. The space in the tube 

 being small, the air is easily saturated with moisture, 

 and the nerve is thus kept for some hours from drying. 

 The free ends of the ring-shaped electrodes are for 

 connecting with the wires from the battery or coil. 



Other forms of electrodes will be noticed farther on 

 in connection with various experiments. In chapter 

 xv. electrodes for use in medicine and surgery are 

 shown. 



CHAPTER VII. 



EXPERIMENTS ON MUSCLE AND NERVE STIMULATION. 



THE muscle telegraph (Fig. 35) of Du Bois 

 Reymond is devised for signalling when a muscle con- 

 tracts, and to some extent to indicate the amount of 

 its contraction. On a rectangular piece of wood gg 

 are two upright pillars. One pillar D supports the 

 forceps A, fixed in a handle B, in and out of the socket 

 of which they can slide and be secured by the screw s ; 

 the other pillar can be approximated to or removed 

 from D by sliding on z. The second pillar has a little 



