MUSCLE-NERVE. 



the muscle of preparation i. Stimulate the nerve of preparatu n . 

 with a tetanizing current from an inductorium. Both muscles will 

 be thrown into tetanus. 



The nerve of the second preparation is stimulated by the action 

 currents of the first preparation. 



The action current is due to a change of potential in an inactive, 

 as compared with an active muscle fibre. The same change may 

 be demonstrated in a nerve over which 

 an impulse is passing. This may be 

 well shown by means of some form of 

 delicate current detector, such as the 

 galvanometer or capillary electro- 

 meter. 



4. The Capillary Electrometer. 

 This instrument, as commonly em- 

 ployed, consists of a capillary tube 

 containing mercury and dipping into 

 a vessel containing sulphuric acid. 

 The surface tension of the mercury is 

 so great that it does not flow through 

 the fine capillary tube, and its upper 

 and lower meniscus is convex instead 

 of concave as is the case with water. 

 The sulphuric acid is connected with 

 a platinum wire. The mercury in the 

 capillary is also supplied with a plati- 

 num wire for connection with any 

 source of current (see Fig. 15). The 

 upper end of the capillary tube is 



connected, through a T tube, with a mercury manometer and with 

 a pressure bottle or syringe bulb. By raising the pressure bottle or 

 pressing on the bulb, pressure is exerted upon the mercury in the 

 capillary tube. This pressure is measured by the manometer. By 

 pressing the mercury in the tube downward and then releasing the 

 pressure, some sulphuric acid is drawn up into the tube, into con- 



FIG. 15. Capillary Electrome- 

 ter. (Lippmann's.) e e, wires 

 leading to source of current ; Hg, 

 mercury in capillary tube; Hy 

 SO 4 , sulphuric acid. 



