88 ELECTRO-PHYSIOLOGY CHAP. 



muscle. From this point of view we are able satisfactorily to 

 explain all the preceding evidence re staircase rise of contractions, 

 and to see in it solely the expression of a general law, according 

 to which not only the physiological capacity for work in any 

 organ (particularly in muscle), but also its morphological develop- 

 ment, which to the last degree is dependent upon nutrition, are 

 conspicuously promoted by regular activity (effect of practice). 

 The degeneration of muscles which from any cause have for a 

 long time been inactive in the body, the pronounced development 

 of the same when in vigorous exercise, afford sufficient proof 

 of the favourable effect of muscular activity upon nutrition. 

 This last is mainly subserved by the regulation of the supply of 

 udcrial blood, as exhibited in vertebrate muscles, which must 

 also, of course, to a greater or less degree control the fatigue 

 effects. Ludwig and Sczelkow observed in 1861 that the 

 blood-vessels of muscles widened in contraction, so that the 

 blood circulates through them more rapidly, and Tiegel (I.e. p. 81) 

 found the same vascular effect in direct excitation of curarised 

 frog's muscle. Such a muscle treated at regular intervals with 

 maximal or sub-maximal stimuli (induction currents) grows more 

 and more reel in the course of excitation, and may even set 

 up extravasculation. The long continuance of the " staircase " 

 rise in height of twitch under these conditions must certainly be 

 referred partly to this hyperaemia ; but we have already pointed 

 out that this is not its sole cause, as is self-evident from its 

 appearance in bloodless preparations. 



The effect of fatigue is, as we have stated, not merely to alter 

 the height of the contraction as described, but also its time- 

 relations, which with progressive fatigue become more and more 

 extended. This retardation of the course of the twitch, which 

 increases gradually during a long series of contractions, and 

 expresses itself more particularly by a considerable extension of 

 the phase of relaxation of the muscles, may finally attain such 

 proportions that even with longer intervals of stimulation lasting 

 for several seconds, the muscle has not time to relax to its 

 original length before the beginning of the next contraction, and 

 thus the base points of each individual curve rise higher and 

 higher above the abscissa, Funke (43) has recorded cases in 

 which the myogram at the later stages of fatigue resembled a 

 steady tetanus curve, although the stimulation intervals lasted 



