n ELECTROMOTIVE ACTION IN MUSCLE 415 



Electromotive action does therefore, under the same conditions, 

 seem at times to undergo a considerable augmentation. If 

 properly excitable gastrocnemii of " cold frogs " are employed as 

 primary preparations, a more or less crowded series of twitches 

 appears - - independent of loading or not loading with slow 

 rhythmical excitation by the make and break of a primary in- 

 duction coil, each of which is also followed by a secondary contrac- 

 tion, so that the beginning of the primary series coincides with 

 that of the secondary series of twitches. And, in conclusion, if 

 primary twitches are summated into a steady, uniform tetanus by 

 accelerated excitation, this is no less the case as a rule with 

 secondary preparations. The primary sets up a secondary co- 

 incident tetanus. The effect is quite different when a warm- 

 blooded muscle is used as the primary preparation, for, when it is 

 unstretched, even the strongest excitation fails to produce secondary 

 twitches. Thus apart from the temporary state of excitability 

 of the preparation it depends solely upon the length of the 

 interval which separates the single stimuli, whether or no the 

 secondary inactivity of the muscle continues during the whole 

 period of incomplete tetanisation. 



As a rule, when the test-nerve is placed upon the surface of the 

 primary muscle, the latter excites the secondary preparation after 

 a longer or shorter series of ineffective twitches. The secondary 

 twitches are small at first, but rapidly increase in magnitude, 

 and may finally far out-top those of the primary preparation. 



Since the contractions of a warm-blooded muscle become 

 more extended at a certain stage of fatigue, at which, more 

 particularly, elongation takes up a longer period, it may happen 

 that with even a moderately rapid succession of single stimuli, 

 the twitches of the unloaded, primary preparation fuse into almost 

 constant tetanus, the vigorous and perfectly distinct secondary 

 twitches alone expressing the internal changes of the muscle, 

 which correspond with each stimulation-impact ; the same occurs 

 also in tensely stretched muscle. It has already been stated 

 that the period for which the unstretched gastrocnemius muscles 

 exhibit secondary activity during incomplete tetanus, is con- 

 ditioned on the one hand by the degree in which the specific 

 muscular state induced by heat is developed, and on the other by 

 the intensity and number of the successive stimuli in the time- 

 unit. Here we need only say that the delay seems generally to 



