THE TISSUES 



47 



This, however, is not a true living contraction. (Practical 

 Physiology, Chap. III.) 



4th. Muscle may also be made to contract by any sudden 

 change in an electric current passed through it, whether the 

 current be suddenly allowed to pass into it or suddenly cut 

 out of it, or whether it is suddenly made stronger or weaker. 

 (Practical Physiology, Chap. II.) 



This method of stimulating muscle is constantly used in 

 medicine. It is a matter of no importance how the elec- 

 tricity is procured, but most usually it is obtained either 



1st. Directly from a galvanic battery ; or 



2nd. From an induction coil. 



FIG. 17. Rheonome, consisting of a circular trough filled with sulphate of 

 zinc solution, into which dip the arras of a bridge which can be brought 

 rapidly or slowly into the proximity of the wires of a galvanic circuit. 



If a galvanic battery is used (1) On making (closing) the 

 current, and upon breaking (opening) the current, a contrac- 

 tion results. While the current is flowing through the muscle, 

 the muscle usually remains at rest ; but if the current is 

 suddenly increased in strength or suddenly diminished in 

 strength, the muscle at once contracts. With strong cur- 

 rents a sustained contraction galvanotonus may persist 

 while the current flows. (Practical Physiology, Chap. II.) 



It is the suddenness in the variation of the strength of the 

 current rather than its absolute strength which is the factor 

 in stimulating, as may be shown by inserting some form of 

 rheonome into the circuit by which the current may be either 

 slowly or rapidly varied (Fig. 17). 



