GENERAL PHYSIOLOGY OF MUSCLE ANU XEHVE. 



49 



fail to irritate a striated or non-striated muscle. A more rapid rise, such as 

 is shown in 6, might irritate a non-striated muscle, but fail to irritate a nerve 

 or a striated muscle. With currents which rapidly gain their full intensity 

 and then return again to zero, the following cases would be possible: A 

 rapid rise and fall of intensity (see c), such as occurs by an induction shock 

 or by the momentary closure of a battery current, might suffice to excite 

 a nerve but not be an effective irritant to a striated, much less a non-striated 

 muscle, unless the short duration of the current were compensated for by 

 a considerable increase in the intensity (see d). On the other hand a form 

 of variation such as is shown in e, where the rate of change is very rapid, 

 although the intensity is not great, might act to irritate nerves, and, because 

 of the longer duration of the current, striated muscles, though having no effect 

 on non-striated muscles ; and the slower rate of change, and considerable dura- 



Fio. 24. .—Schema of relation of the method of application of the electric current to the 



irritating effect. 



tion, illustrated by/, though not affecting nerves, might suffice for striated 

 muscles and be favorable to the excitation of non-striated muscles. 



In the case of nerves, duration of current is less important than a rapid 

 change of intensity. In the case of striated muscles the advantage to be 

 gained by rapid variations can be easily overstepped, and the importance of 

 the duration of the current is greater; while in the case of non-striated muscles 

 duration of current is of the first importance and rapid variation may tail to 

 excite. In the case of all tissues, strength and density of current, what we 

 may call intensity of current, is favorable to excitation. 



(/) Effect of tin 1 Direction in which the ( \wreni flows along the Neme. — 

 The result of the irritating change produced in a nerve by a battery current 

 has been found to depend upon whether the current Hows toward or away 

 from the organ stimulated by the nerve. This fact can be most readily ob- 

 served in the ease of isolated motor nerves. In the case of these nerves, the 

 effects produced by opening and closing the current are different according as 

 the current is descending, i. e. flows through the nerve in the direction of the 

 muscle, or ascending, i. e. flows through the nerve in the opposite direction. 

 Vol. II.— I 



