ADVANCED EXPERIMENTAL PHYSIOLOGY 121 



end of the muscle with a hot wire. The muscle is now stimulated 

 by a tetanising current applied to its uninjured end ; the deflection 

 of the galvanometer is in the reverse direction, due to the current of 

 action (formerly called the negative variation) which is produced 

 when the muscle contracts. 



The current of injury is, as Gotch pointed out, to be considered 

 as a local current of action ; around the injured portion the tissue 

 is in a condition of excitation. 



Similar experiments are demonstrated upon nerve. 



String-galvanometer Electro-cardiograph. The student should 

 read the description of this instrument in his Text-book of Physi- 

 ology. 



Lippmann's Capillary Electrometer. This instrument is a delicate 

 electrical manometer, and is more suitable than the galvanometer 

 for the investigation of the electromotive pro- 

 perties of the frog's heart ; it responds to very 

 rapid changes of electrical potential. It consists 

 (Fig. 122) of a glass tube C drawn out at one 

 end to a fine capillary tube ; this is filled with 

 mercury and is connected with a pressure 

 apparatus by the rubber tubing ET. The 

 capillary tube dips into a small trough filled 

 with 10 per cent, sulphuric acid ; the bottom of 

 this vessel is covered with mercury M in order 

 to provide good electrical conduction with the 

 platinum wire. The movements of the column 

 of mercury in the capillary tube are observed by 

 means of a microscope fitted with a micrometer 

 scale. 



The passage of an electrical current through FIG. 

 the capillary tube alters the surface tension, 

 and this alteration causes a movement of the 

 mercury in the capillary tube. The movement 

 of the column of mercury is from positive to negative, and the ex- 

 tent of the movement is roughly proportional to the difference in 

 electrical potential. Based upon these facts are the determination 

 of the direction of, and the measurement of the electromotive force 

 of, the current which is under investigation. 



With the capillary electrometer the electromotive properties of the 

 frog's heart are demonstrated. The base and the apex of the 

 ventricle are led off by unpolarisable electrodes to the electrometer : 

 each time the heart contracts there will be a diaphasic variation, 

 the contracted portion at first becomes negative and then positive 

 to the uncontracted part. 



122. Diagram 

 of the capillary 

 electrometer. 



