12 



PHYSIOLOGY 



CHAP. 



The study of fatigue phenomena in muscle is simplified and 

 made more complete if, instead of sending in the excitations at 

 regular intervals, the muscle is stimulated by a make induction 

 shock directly it has relaxed. The apparatus can be arranged so 

 that the contraction of the muscle breaks the exciting circuit, and 

 its relaxation closes it again. The muscle thus contracts and 

 relaxes continuously (Wundt, 1858 ; Novi, 1879). 



Fig. 7 shows the curve of muscular fatigue passing into 

 complete exhaustion. It exhibits the initial phases that are to 

 be seen in Waller's incomplete curve, followed by a much longer 



Fio. 7. Complete tracing of muscular fatigue from frog's gastroenemius ; series of successive 

 contractions which vary in frequency with the varying duration of the contraction. (I. Novi.) 

 Lines 1, 2, 3, 4 represent successive parts of one tracing, a, b, first, very brief phase con- 

 sisting of extremely rapid contractions of increasing height ; 6, c, second phase, four to five 

 times longer, rapid contractions decreasing in height ; c, d, third phase, less rapid contractions, 

 approximately equal in height ; d, c, fourth phase, longer than preceding, contractions becoming 

 slower and higher ; e, f, fifth phase, the longest of all, contractions decrease regularly in height, 

 and become increasingly slower ; x, y, slowest of all ; y, f, minimum height, contractions 

 gradually die away. 



final phase, in which the height of the twitches regularly decreases 

 in a straight line, as shown by Kronecker. 



By Novi's method it is easier to analyse the changes in the 

 functions of muscle which are due to fatigue, and the variations 

 of the curve of fatigue with variations of temperature, and under 

 the influence of different drugs and poisons. 



When fatigue has been pushed to complete exhaustion by 

 very frequent stimulation the muscle often fails to regain its 

 normal length, and remains more or less contracted, thus approxi- 

 mating to the state of rigor that signalises its death. 



If the muscle is left to itself for a certain time after its 

 excitability is so exhausted that it no longer reacts to stimuli, 

 it gradually recovers, i.e. regains its excitability. In the living 



