II CHANGE OF FORM IN MUSCLE DURING ACTIVITY 87 



muscle-substance is completely compensated by the A-process. 

 In other cases (with greater stimulation-frequency), it is perfectly 

 intelligible that a progressive fatigue and decrement of the magni- 

 tude of contraction must ensue. The only point that is difficult 

 to elucidate is the initial staircase increment of the twitches, more 

 especially in excised, bloodless muscle, which seems in direct 

 contradiction with the previous theory. It is clear that we 

 could only come to a right understanding of this phenomenon 

 if the A-process, the invariable concomitant of the D-process, 

 were more taken into account than has been customary in 

 physiology. There are countless instances in which we may 

 observe that living matter after undergoing the " down " change 

 consequent on a D-stimulus, i.e. falling below par, returns from 

 this state to the earlier at par of autonomous equilibrium, which 

 " recovery " (due to preponderance of A over D) proceeds with 

 so much the greater energy in proportion as the magnitude of the 

 " down" change, caused by the preceding stimulus, has been greater. 



It is possible that we have in this the interpretation of the 

 fact mentioned above, that muscle fatigues more slowly with 

 maximal than with sub-maximal rhythmical excitation. In any 

 case, the living matter alters after each cessation of a D-stimulus 

 in virtue of its inherent energy, in a sense inverse to its action 

 during the stimulus, i.e. in an " ascending " direction. The " re- 

 covery " of such living substance, " fatigued " by excitation, is 

 always an " autonomous ascending alteration," by which the 

 depreciation of matter is compensated, and it is brought back to 

 par, as previous to excitation. 



It would further appear that, under favourable conditions, 

 the " down " change of substance produced by a D-stimulus is 

 followed by such an energetic " up " change that the much 

 accentuated A-process becomes not merely at, but above, par 

 when it is of course succeeded by an augmented D-excitability. 

 Such a rhythmical series would denote, not that the living sub- 

 stance (e.g. cardiac muscle) in equilibrium, alternated regularly in 

 " up " and " down " changes between D and A, when the preceding 

 "down" change would be completely compensated during the 

 period of the " up " change, nor that there was a " down " change 

 in the value of the substance ("fatigue"), but, on the contrary, 

 that there was an ascending alteration, as expressed in increase of 

 capacity for work and augmentation of height of twitch in the 



