ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 71 



blooded muscle, Kichet in the muscles of crab, and Romanes in 

 medusa (24). If uniform induction currents are sent rhythmic- 

 ally through the resting apex of the frog's heart, a ladder, or 

 "'staircase," of contractions with increasing amplitude is almost 

 invariably exhibited, as shown in the accompanying series of 

 curves (Fig. 37). 



Tiegel (I.e. p. 37) observed an analogous effect in curarised 



FIG. 37. Heart (Frog) artificially excited after ligature of the sinus. The first notch of each curve 

 is produced by the auricular, the proper summit by the ventricular systole. Both exhibit 

 the staircase. (Engelmann.) 



frog muscles (gastrocnemius) with intact circulation. If single 

 induction shocks of uniform strength are sent into such a muscle 

 at regular intervals, the height of contraction increases constantly, 

 so long as maximal stimuli are employed, even in a series of 

 several hundred contractions, so that the height of the " stair- 

 case " (i.e. the curve which unites the joint summits of an ascend- 

 ing series of contractions) increases within certain limits with 



FIG. 38. Excitation of a somewhat exhausted bloodless gastrocnemius of Frog, by groups of 

 1, 2, 3, 4, 5, uniform maximal break induction shocks. Increase in height of contraction 

 with repeated excitation at short intervals ("staircase"). Decrease on longer duration of 

 the pauses (tuning-fork, ^ sec.) (Engelmann.) 



the strength of the individual stimuli. On the application of 

 minimal stimuli, there is, as a rule, no increment of the contrac- 

 tion series, or at most a trace only, whereas in the maximal 

 series it is invariably well developed (Fig. 38). If such a series 

 is interrupted and resumed after a pause, the first of the new 

 contractions is smaller than the last before the interval (Tiegel, 

 Eossbach, Buckmaster), but the muscle immediately resumes its 

 increasing contractions. Within a certain range it is absolutely 



