70 PHYSIOLOGY CHAP. 



Du Bois-Keymond's researches began in 1841, shortly after 



Fio. 43. Thomson's galvanometer. To the left is the galvanometer, in the centre a shunt, to the 

 right the scale, illuminated by a beam reflected from a lamp to the galvanometer mirror. 



those of Matteucci. He devoted many years to the study of 

 animal electricity, and his great merit lies 

 in the introduction of exact methods. His 

 discovery of unpolarisable electrodes, com- 

 bined with the method of compensating 

 by means of a rheochord, enabled him to 

 separate the tissue currents from those of 

 metallic origin, and to measure them, both 

 in the resting state of the muscles and 

 nerves and during their activity. 



In 1867 Hermann's investigations 

 opened up a new chapter in electro- 

 physiology. He overthrew du Bois- 

 Keymond's theory, according to which 

 electrical currents are pre - existent in 

 normal living tissues in the resting state 

 (" pre-existence theory"). By the experi- 

 ments we are about to discuss, which were 

 to a large extent confirmed by subsequent 

 observers (Hering, Engelmann, Bieder- 

 mann, and others), Hermann proved that 

 muscles and other tissues, so long as 

 they are at rest and intact, give off no 

 currents to the galvanometer. When 

 currents appear they are due solely to 

 the effects of artificial alteration of the 

 tissues, or to the disturbance of chemical 



equilibrium which accompanies functional activity (" alteration 



theory "). 



Fio. 44. Diagram of galvano- 

 meter, n s and s n, pair of 

 magnets with opposite poles, 

 circular mirror tixed to upper 

 magnet ; 1 1, end of wire that 

 surrounds the magnets ; N S, 

 third magnet, which controls 

 the two lower magnets. 



