422 ELECTRO-PHYSIOLOGY CHAP. 



changes in intensity and duration of the action current in the 

 primary muscle, which must be regarded as fatigue effects, as is 

 attested by the reappearance of secondary tetanus, when the 

 primary muscle has had a certain time to recuperate. Thus 

 Morat and Toussaint (54) observed secondary initial twitches, 

 with fatigue of the primary muscle, at a frequency of 70-80 

 stimuli per sec. Where fatigue is as much as possible eliminated, 

 secondary tetanus may be kept up by strengthening the primary 

 excitation, within a wide range of frequency. 



While the primary tetanus discharged by rhythmical excita- 

 tion, electrical or mechanical, does for the most part elicit 

 secondary tetanus also (though not always coextensive in duration), 

 in other forms of artificial tetanus this never is the case ; although 

 in favourable examples secondary twitches may be elicited. As 

 we shall see later, striated skeletal muscle falls, under certain 

 conditions, into prolonged tetanus while the nerve is traversed 

 by a constant current (closure tetanus), and occasionally after 

 the opening of the circuit also (Eitter's opening tetanus). J. J. 

 Friedrich (55) found that the secondary preparation in such a 

 case responded only, if at all, by a secondary twitch at the 

 commencement of the tetanus under observation, never by a 

 secondary tetanus. It is, moreover, remarkable that the effect 

 was much more often absent in opening, than in closure, 

 tetanus. 



The tetanus induced by chemical excitation of motor nerves, 

 though often pronounced, is equally inefficient as regards second- 

 ary tetanus (Kiihne, I.e. p. 61 f.) Salt tetanus and glycerin 

 tetanus produce, as Kuhne says, such a large mechanical yield of 

 work from the muscle, that the failure of secondary tetanus 

 cannot certainly be ascribed to weakness of muscular excitation ; 

 it must rather be owing to the local mode of attack of the 

 chemical stimulus, or to its temporal relations, that the muscle 

 responding indirectly to it exhibits such a different reaction. 



This is the more remarkable since every mode of vital tetanus 

 yields at most one or more secondary initial twitches, or inter- 

 mittent secondary intermediate twitches, never secondary tetanus. 

 Du Bois-Eeymond investigated the question " whether strychnia 

 tetanus, like electrical tetanus, is of an interrupted character " ; 

 he arranged his experiment so that the test-nerve was applied 

 to the natural longitudinal, and natural or artificial transverse 



