ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 83 



that the summit of the latter lies much nearer to the initial 

 point than the summit of the isotonic curve, i.e., in other words, 

 with constant length the muscle reaches the maximum of tension 

 much sooner than with constant tension it reaches the maximum 

 of shortening (Fig. 42). 



IV. EFFECT OF FATIGUE UPON THE PROCESS OF MUSCULAR 



CONTRACTION 



The most fundamental sign of distinction between living and 

 dead matter is undoubtedly that of Metabolism, i.e. chemical 

 processes taking place within the living matter. By these 

 certain substances are produced, on the one hand, which are 

 finally excreted as useless to the organism, while, on the other, 

 nutritive substances are taken up and assimilated. With Hering 

 we may call the former process " dissimilation," the latter " assimi- 

 lation." Bering's conclusions as to these two fundamental pro- 

 cesses of metabolism are so important to our subject as to demand 

 a full exposition, and this is best given in his own words (40). 

 " Assimilation and dissimilation must be conceived as two closely 

 interwoven processes, which constitute the metabolism (unknown to 

 us in its intrinsic nature) of the living substance, and are present 

 simultaneously in its smallest particles, since living matter is neither 

 permanent nor quiescent, but ever more or less in constant motion. 

 It is a fundamental property of living matter, engrained deeply in 

 its nature, to assimilate and dissimilate ; and these processes 

 continue, provided only the essential conditions of life are present, 

 without assistance from external stimuli." In so far as living 

 matter is wholly unaffected by the occasionally working external 

 stimuli, Hering designates its assimilation (A) and dissimilation 

 (D) as "autonomous." 



" So long as the autonomous D and A are equal in ratio, 

 the state of living matter cannot be altered, and it remains the 

 same qualitatively and quantitatively." This state of perfect 

 equilibrium between the autonomous D and A is termed by 

 Hering " autonomous equilibrium." 



" This condition of living matter is altered when any stimulus 

 incites it to active dissimilation, which is not balanced by equal 

 assimilation. Under these conditions D is no longer exclusively 

 autonomous, but is reinforced by outside factors ; it may there- 



