Ill 



ELECTRICAL EXCITATION OF MUSCLE 



179 



may last a minute, and the muscle remain nearly as long in a 

 state of maximal shortening, when excited by weak as well 

 as by strong currents. The dependence of contraction magni- 



LjLLJLJLLlJULjJ_JJL^^ 



FIG. 74. Closure contraction of adductor muscle of Anodonta (excitation by the constant 

 current) ; (s), closure ; (o), opening. 



tude on duration of closure is most plainly seen on the prepara- 

 tion in question if the circuit is opened before the maximum of 

 shortening is reached. Constant currents which produce maximal 

 contraction of the muscle when closed for 3-4 sees, often effect 

 a merely insignificant shortening if closed for only J sec. At 

 this range the closure contraction is greater with unaltered 



FIG. 75. Etfect of duration of current on contraction magnitude of adductor muscle of Anodonta 

 (excitation with constant current) ; (ft), duration of closure = J sec. ; (6), = 1 sec. ; (c), = 4 sees. ; 

 (o), opening contraction. (Biedermann.) 



strength of current in proportion with the time during which cur- 

 rent passes (Fig. 75). This agrees with the fact that single induc- 

 tion shocks only stimulate the most excitable preparations at a 

 very high intensity, so far as may be concluded from the visible 



