CHANGE OF FORM IN MUSCLE DURING ACTIVITY 



77 



fulcrum pulls on the same lever in the opposite direction such a 

 contraction is termed " isotonic " (Fick) (Fig. 40). It will 

 then be found as a rule that, with heavy loading, the height of 

 such contractions decreases gradually with the magnitude of the 

 constant tension, rapidly at first, and afterwards much more 

 slowly, but by no means in proportion with the loading, so that the 

 corresponding yield of work increases simultaneously without inter- 

 ruption (cf. Santesson's tables, Scandinamschen Archiv, i. 1889, p. 

 2 5 f.) Under certain conditions a direct increase in magnitude 

 of contraction (height of twitch) is visible with increasing 

 tension. As early as 1863, A. Fick observed in the adductor 



FIG. 40. Isotonic Method. (Gad.) 



muscle of Anodonta, which consists of uninuclear fibre -cells, 

 that the height of lift increased with increase of loading ; Heiden- 

 hain asserted the same paradoxical fact in tetanising striated frog 

 muscle, and later on it was also determined for single twitches 

 by different experimenters, provided that during the isotonic 

 process the load is not excessive (Fick, Marey, v. Frey, 32). 

 More especially in the case where the tension of the muscle in 

 contraction increases constantly, or from a given moment (e.g. 

 when the muscle pulls on an elastic spring), the shortening will 

 be greater with stronger, than with diminished, initial tension. 

 This fact was indeed established by Fick when he showed 

 that if a muscle is appropriately hindered in shortening, and the 



