ii . CHANGE OF FORM IN MUSCLE DURING ACTIVITY 99 



same effect on single twitches, as in isotonic experiments. The 

 only difference is in the form of the apex of the contraction 

 curve. All isotonic curves are dome -shaped at the summit, 

 i.>: diminution of the ordinates begins directly the maximum 

 has been reached. In isometric curves, on the contrary, a 

 plateau is formed by the interval between temperature of the 

 room and freezing-point, at the summit of contraction, i.e. the 

 maximum of tension remains constant for a longer or shorter 

 time after it has reached its climax. 



These striking effects of temperature upon the height and 

 course of contraction in striated skeletal muscle seem to indicate 

 that two different processes come into play during muscular 

 activity, which are opposed to one another, and are differently 

 affected by fall of temperature. Fick pointed out that a specific 

 (chemical) process lies at the root of muscular relaxation, 

 essentially differing from and opposite to that underlying con- 

 traction. The ordinates of the contraction curve are therefore 

 not proportional to the intensity of one process, but express the 

 results of two antagonistic processes. Fick suggests that the 

 first of these may consist in the formation of a specific substance 

 (decomposition of sugar into lactic acid), the second in the 

 further disintegration of the resulting product (breaking up of 

 lactic acid into H O and CO.,). The acid produces a partial 

 coagulation of the contents of the sarcolemma, which is 

 reduced again by removal of the chemical causes. Gad and 

 several of his pupils, as also Schenk, have recently worked out 

 this idea and applied it to the explanation of the phenomena 

 under consideration (33). Here we need only say that the 

 same conclusions follow naturally from Bering's general principle, 

 and that it would be possible to explain all the phenomena 

 observed on the supposition that change of temperature exerts a 

 more depressive influence upon one of the fundamental processes 

 of metabolism than upon the other. 



On the hypothesis that the active " process of relaxation " 

 in Fick's sense goes hand in hand with the process of assimilation, 

 some value may attach to the observations of Fr. Schenk (61), 

 i.e. that relaxation occurs more slowly in proportion with the 

 scarcity of reserve substances in the muscle. On comparing an 

 actively fatigued muscle with one whose excitability has been 

 depressed by irrigating it with a solution of lactic acid, without 



