364 THE PROPERTIES OF STRIPED MUSCLE. 



appeared to Professor Fick necessary that the whole subject of the 

 mechanical conditions which affect muscular activity, especially with 

 reference to their influence on the terminal stage, should be worked out, 

 his pupil and assistant, Dr. Schenck, 1 has with infinite perseverance 

 subjected these conditions to experimental investigation. Eegarding 

 resistance to shortening as the most important of them, he aims at 

 showing how the tension so produced acts directly on the two processes 

 which he supposes to be concerned in the twitch " the one which 

 causes shortening, and the one which effectuates relaxation" 2 the most 

 characteristic effect of tension being, according to him, that it hastens 

 the supervention of the "second process." Schenck regards the two 

 processes as complementary to each other, and consequently holds that 

 any alteration of the intensity or time-relations of either constituent 

 process must affect the character of the whole. Whilst this view was 

 being set forth at Wiirzburg, under Tick's immediate influence, Professor 

 Gad of Berlin, and his pupil Kohnstamm, had been led by Tick's 

 previous suggestions to speculate in a very similar direction. There are, 

 according to them, 3 two processes by which energy is transformed in the 

 muscular response to stimulation. Both are heat-producing, but the 

 first, which is associated with contraction, more so than the second, 

 which is associated with relaxation. Both are favoured more or less by 

 increase of temperature, as well as by increased intensity of stimulus, but 

 the first only is favoured by increase of tension. The difference 

 between the two theories lies in the fact that Gad does not recognise 

 what appears to be Schenck's fundamental notion, namely, that whenever 

 a muscular contraction is resisted, the action of the primary instan- 

 taneous stimulus is supplemented or reinforced by a second stimulation, 

 having its source in the tension which the resistance produces. Both 

 authors show that the course (order of phenomena) of the excitatory 

 process can be modified during its progress by external conditions, 

 and think that these modifications can be best understood by 

 supposing that the process itself is dual, i.e. that it is made up of two 

 constituent processes, more or less antagonistic to each other, and that 

 the effect of resistance in modifying the course of the excitatory process 

 depends on its influence on the two constituent processes. 



The sketch I have given of these speculations, although scanty, 

 may serve the purpose of facilitating the understanding of the very 

 remarkable influence of tension on the excitatory process, of which the 

 experiments made during the last half-dozen years by v. Kries, Schenck, 

 Gad, Kaiser, and others, give evidence. The examination of these 

 observations will afford us the opportunity for such theoretical com- 

 ments as may appear necessary. 



Methods and instruments. In Helmholtz's original myographic method, 

 the changes recorded were partly of length, partly of tension. Marey was the 

 first to show that, if it is desired to register changes of length correctly, very 

 light writing-levers 'must be used, so as to avoid the errors arising from 

 inertia ; and it was he who taught us how to obtain myograms, the forms of 

 which approach that of the true isotonic curve. Then, twenty years ago, Fick, 

 by discovering and showing how to apply the isometric method, opened a new 

 line of inquiry. His first tension-writer (represented in Fig. 190, p. 355) was 



1 Arch. f. d. ges. PhysioL, Bonn, 1891, Bd. 1. S. 166 ; 1892, Bd. Hi. S. 117. 



2 Schenck, ibid., Bd. Iv. S. 626. 



3 Gad, Arch. f. PhysioL, Leipzig, 1893, S. 170. 



