84 ELECTRO-PHYSIOLOGY CHAP. 



fore be denoted as allonomous, in distinction from the purely 

 autonomous process. The increased formation of D- products, 

 and corresponding loss of elements which were formerly an 

 integral part of the living matter itself, and entered into its 

 chemical composition, produces intrinsic alteration in the sub- 

 stance in proportion with the strength and duration of the stimulus. 

 Hence at the close of excitation the substance is found to be 

 quantitatively and qualitatively altered." 



If the D-process is regarded as a function of living matter, it 

 must at this stage be designated as less capable of functioning. 

 Since the substance is altered, not merely qualitatively but quan- 

 titatively also, its state, after the action of a D- stimulus, as 

 compared with its earlier condition, may in Bering's terms be 

 denoted as " below par " ; obviously, therefore, as soon as the 

 D-stimulus begins to act, the depreciation of the living matter 

 proceeds pari passu, increasing with the duration of the excitation. 

 The potential dissimilation of the substance, however, diminishes 

 in the same ratio. 



This accordingly denotes that excitability diminishes in pro- 

 portion with the duration of the D-stiinulus, or, as it is usually 

 expressed, the substance fatigues itself. This indisputable action 

 of every D-stimulus may be further reinforced in its physiological 

 effect by an aggregation of disintegration, or dissimilation, products, 

 which, beyond a certain limit, are in many cases demonstrably 

 inimical to the functions of the living matter. 



The manifestations and laws of " fatigue " were first investi- 

 gated in cold-blooded muscle (excised, or in situ) by Kronecker 

 (41) and Tiegel (24) ; in. warm-blooded muscle by Kossbach (24) ; 

 and, recently, in man by Mosso (42). A number of conclusions 

 have been reached, some at least of which must be quoted. 



Muscular fatigue is indicated experimentally by the greater 

 strength of stimulation required in order to produce a constant 

 yield of work, i.e. same height of lift in contraction as in the 

 unfatigued state, or, conversely, by the decrease of lift, or yield 

 of work, with constant stimulation. If the muscle is excited 

 rhythmically at constant intervals, with uniform maximal stimuli 

 and resistance by single induction shocks, a double alteration 

 of the contraction curve is seen in height and in duration. 

 Kronecker found in frog muscle that the lift diminishes regularly 

 from twitch to twitch, and that by a constant fraction of de- 



