ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 121 



tote," which is the more remarkable since the increment of 

 single twitches in the "staircase," as well as with increasing strength 

 of stimuli, follows the same law ; yet the rule can hardly be 

 universal, e.g. the tetanus curve of hydrophilus muscle does 

 not coincide with it (Eollett, 8). The difference of contraction 

 magnitude is at once apparent on comparing the two cases of 

 complete tetanus resulting from a series of maximal induction 

 shocks, and a single contraction. The freely contracting, loaded- 

 muscle invariably shortens more in tetanus than in a single twitch. 

 Even if it were certain that the greater height of tetanus may be 

 explained by the superposition (as described) of single twitches, 

 the subsequent course of the process remains in obscurity. We 

 can only conclude from the fact that the muscle in tetanus 

 does not exceed a certain maximal shortening, that Helmholtz's 

 law loses more and more of its significance with progressive 

 superposition, each new stimulus being so much the less effective 

 in proportion as the muscle has already shortened with the pre- 

 ceding stimuli. The height of the tetanus curve grows with the 

 strength of excitation, or, where this is constant, with its frequency. 

 The steepness of the rise alters in the same proportions (Kohn- 

 stamm, 9). 



A fact of great importance in the estimation of tetanus was 

 determined by v. Kries and v. Frey (10), who showed that arti- 

 ficial support of the muscle would, under some conditions, pro- 

 duce the same degree of contraction from a single stimulus, as in 

 complete tetanus. In this experiment an adjusting screw is 

 placed under the muscle-lever, and so arranged as to raise it 

 to any given height. The loading first takes effect fully upon 

 the muscle, when it begins to raise the lever from the support. 

 The fact that the supported muscle contracts as vigorously in a 

 single twitch, as the unsupported muscle in the more pronounced 

 tetanus, is very apparent when single twitches and tetani are 

 alternated in the same experiment. If the muscle is sufficiently 

 loaded, the tetanus curve rises more or less above the summits of 

 the single twitches of the unsupported muscle. If the tetanus 

 is followed by a row of "propped" twitches (Fig. 55, a) the 

 parallelism of the two processes is very apparent, and the con- 

 viction is forced upon us that in summation of twitches in muscle 

 there must be some kind of under-propping in the muscle ; the 

 effect is, as Grlitzner (11) says, " as though the muscle contracted 



