GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 57 



changes, the greater the irritating effect upon nerves. Not all nerves, however, 

 are equally susceptible to rapid alterations of the intensity of the current! 

 Non-medullated nerves do not appear to react as readily as medullated to 

 electric currents of short duration. For instance, the nerves of the claw mus- 

 cles of the crab are not readily excited by induced currents, and respond better 

 to the more prolonged influence of the closing and opening of battery currents. 1 



The question now arises, Is the reaction of muscles to electric currents the 

 same as that of nerves ? Experiment shows that muscles which have been 

 removed from the action of nerves, by means of curare, differ from medullated 

 nerves in that they are excited more vigorously by the opening and closing of 

 battery currents than by making and breaking induction currents. The max- 

 imal contraction got on opening and closing a battery current is both higher 

 and more prolonged than that to be obtained with a single induction shock. 

 Unstriated muscles exhibit this difference to a still greater degree than 

 striated muscle ; they react well to the closing of battery currents of medium 

 strength, provided these last some little time, but respond to induced currents 

 only when they are very strong. Thus the unstriated muscle which closes the 

 shell of some of the fresh-water mussels, as the Anodonta, gives larger and 

 larger contractions as the duration of the current is increased from one-quarter 

 of a second to three seconds. Much the same is true of the unstriated muscles 

 of the ureters; 2 the battery current must remain closed quite a while for the 

 closing contraction to be called out, the length of time depending upon the 

 strength of the current ; and induction shocks have little or no effect unless 

 very strong. Such a comparison makes it evident that the duration of the 

 current is an important element in the influence exerted by electric currents 

 on various forms of protoplasm. Unstriated muscles require that the current 

 shall last from one-quarter of a second to three seconds to produce maximum 

 contractions. Striated muscles require that a current shall last 0.001 second 

 (Fick), and even medullated nerves fail to react if the current lasts too short 

 a time. Various forms of irritable tissue can be arranged in series according 

 to their ability to respond to electric currents of short duration, viz. medul- 

 lated nerves, non-medullated nerves, striated muscles, non-striated muscles, 

 and the little-differentiated forms of protoplasm of many of the protozoa. 

 On the other hand these tissues are found to respond in the reverse order to 

 currents which are more prolonged and which change their intensity slowly. 

 It would seem as if the less perfectly differentiated the form of protoplasm, 

 the less its mobility and its susceptibity to passing influences. 



The same form of tissue reacts differently in different animals. For instance, 

 the sluggish striated muscles of the turtle do not respond as well to induced 

 currents as the more rapid striated muscles of the frog. Further, the condition 

 of the tissue at the time is found to have an influence on its irritability and its 

 power to respond to stimuli of short duration. Von Kries reports that nerves, 

 if cooled, react better to slow variations in the intensity of the electric current, 



1 Biederraann : Elektrophysiologie, 1895, Bd. ii. p. 546. 



2 Engelmann: P/%er's Archiv, 1870, Bd. iii. p. 263. 



