ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 89 



several seconds. But the curve of contraction in fatigued muscle 

 is not merely characterised by greater or less extension ; its form 

 also is modified, especially in the descending portion. Generally 

 speaking, this change may be denned, with Fuuke, by saying 

 that the descending portion of the curve gradually loses its 

 character of a free fall, owing to the resistance engendered 

 by fatigue and increasing with it, on which the lengthening of 

 the muscle is more and more retarded, and always in earlier 

 stages, by the weight raised by its own gravity. In the end, as 

 Funke has aptly expressed it, the muscle resembles a viscous, 

 doughy mass, responding with the utmost inertia to the traction 

 which endeavours to bring it back to its original dimensions. 

 The ascending portion of the curve, on the other hand, loses little 

 of its steepness, even when fatigue is carried to exhaustion. The 

 shorter the intervals between the single twitches, the more rapid 

 will be not merely the diminution in contraction magnitude, 

 but also the extension and change of form in the curve as 

 described above. In individual cases, the stage of relaxation in 

 otherwise normal, non-fatigued, striated muscle is conspicuously 

 lengthened, so that, as first described by Kronecker (44) and 

 subsequently investigated by Tiegel (45), the muscles may remain 

 considerably shortened during long pauses (up to 10 sec.) in 

 a rhythmical series of simple induction shocks. It is evident 

 that this phenomenon, which Tiegel terms " contracture," can 

 have nothing to do with fatigue, since with increased function of 

 the muscle it diminishes instead of increasing. In this condition, 

 which, as Tiegel found, is only developed in direct muscular 

 excitation, the excitability of the muscle to normal stimulation 

 rid nerve is minimal, while the contracture may correspond 

 with the height of the twitch. The muscles of spring-frogs seem 

 especially prone to contracture, which then appears even with 

 unimpaired circulation, and is the more marked in proportion 

 with the intensity of excitation (cf. also Mosso, I.e.} 



The course and process of the manifestations of fatigue must 

 obviously be in the highest degree susceptible to all those data 

 on which depend the assimilation, or dissimilation, of muscle- 

 substance. Here, in the first place, we must consider the original 

 physiological condition in which the muscle begins its fatigue- 

 task, the widely varying range of its " capacity for work " and 

 " excitability " in normal connection with the organism, or after 



