ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 125 



attention to the remarkable physiological differences between red 

 and pale muscles in the rabbit, and more particularly to the 

 enormous differences which he found in the stimulation-frequency 

 required to produce tetanus, while Kroiiecker and Stirling (14) 

 subsequently ascertained that the red muscle of rabbit, in corre- 

 spondence with the sluggish process of contraction, is thrown by 

 4 stimuli per sec. into incomplete, by 10 per sec. into 

 fairly complete, tetanus. With stimulation intervals of ^ sec. 

 the pale muscle recovers its extension again almost completely, 

 while the red, though trembling, remains tensely contracted. 

 The pale muscle of rabbit requires from 20 to 30 stimuli for 

 complete tetanus. Analogous curves are obtained from corre- 



FIG. 58. Tetanus curve of tail- and claw-muscles of Crab with uniform excitation. The quick 

 tail-muscles fall into incomplete clonic tetanus, the sluggish claw-muscles into complete 

 tetanus. (Richet.) 



spending excitation of the quick tail- and sluggish claw-muscles 

 of the crab (Eichet, 4) (Fig. 58). 



Very characteristic, and functionally weighty, differences of 

 tetanus contraction were found by Eollett (8) in the anatomically 

 and physiologically different muscles of hydrophilus and dytiscus. 

 Besides the fact that in this case also the quick, rapidly-contract- 

 ing muscles of dytiscus require a higher stimulation-frequency to 

 enable them to contract than the sluggish muscles of hydro- 

 philus, as at once appears from Fig. 59, a, b, another important 

 difference exists in the course of a prolonged and complete 

 tetanus. The first tetani yielded by freshly-prepared dytiscus 

 muscles rose more steeply, and fell much more rapidly, than 

 those of hydrophilus muscles, in which the long duration of 



