148 ^V AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



obtainable from muscle, 0.06-0.08 volt, represents only about 80 per cent, of 

 the true electro-motive force of the muscle-currents, because only a part of 

 the current is led off to the galvanometer, the rest being short-circuited 

 through the fluids surrounding the muscle-fibres, and in the sheath of the 

 muscle. 



The fact that there is a difference in electrical potential between the 

 normal longitudinal surface and the injured cross section of the muscle can 

 be ascertained by the use of the " physiological rheoscope," as the nerve- 

 muscle preparation is called. If the nerve of a fresh nerve-muscle prepara- 

 tion be allowed to fall so as to suddenly close a circuit between these two 

 parts of the muscle, an electric current will flow through it, it will be ex- 

 cited, and the muscle will contract. A muscle can even be made to stimu- 

 late itself by its demarcation current, if some point on the equator be sud- 

 denly connected with a fresh cross section by a good conductor. 



Theories as to Cause of Currents of Rest. — Du Bois-Reymond, impressed by 

 the facts which lie had ascertained as to the direction of action of the electro- 

 motive forces exhibited by the muscle, tried to explain the difference in elec- 

 trical tension of the surface and cross section on the supposition that the 

 muscle was composed of electro-motive molecules which presented differences 

 in electric tension similar to those shown by the smallest particles of muscle 

 which it is possible to study experimentally. Further, he considered these dif- 

 ferences in tension, and the consequent electric currents, to exist within the 

 normal muscle — the longitudinal surface and normal cross section, i. e. the 

 point where the muscle-fibre joins the tendon, having the same sort of differ- 

 ence in electric potential as the normal longitudinal surface and the artificial 

 cross section. When the muscle is injured the balance of the electro-motive 

 forces within is lost, and they are revealed. It is difficult to refute such a 

 theory by experiment, because our instruments only record differences in tension 

 at points on the surface of the muscle to which we can apply the electrodes. 

 We cannot say that there is an absence of electric tension or lack of electric 

 currents within the normal resting muscle; we can only say that there is no 

 direct experimental evidence of the existence of such currents. 



Another theory of the electrical phenomena observed in muscle, and one 

 which has found many adherents, was advanced by Hermann. 2 According to 

 Hermann's view there are no differences in electric potential and no electric 

 currents within the normal muscle; the "current of rest" is a "current of 

 injury," a "demarcation current," i. e. it is due to chemical changes occurring 

 in the dying muscle-tissue at the border line between the injured and living 

 muscle-tissue. 



A It In ugh the greatest differences in potential are observed when many muscle- 

 fibres are injured, as when a cut is made completely through a muscle, injury 

 to any part causes that part to become negative as compared with the rest. 

 Even an injury to a tendon causes a difference in potential. It is exceedingly 



1 Du Bois-Reymond : OesammdU Abhandlungen, 1877, Bd. ii. S. 319. 

 7 Hermann : Handbuch der Physiologie, 1879, Bd. i. S. 235. 



