32 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



two summits, that is, after the first shortening there is a brief 

 relaxation followed by a second, slower contraction. The cause 

 of this second shortening is not known. Biedemann has sug- 

 gested that it is due to the presence in the muscle of the two kinds 

 of fibers red and pale which were spoken of on p. 19, and that 



Fig. 13. Curve showing the effect of veratrin. 



the veratrin dissociates their action, but this explanation, ac- 

 cording to Carvallo and Weiss,* is disproved by the fact that 

 muscles composed entirely of white or red fibers show a similar 

 result from the action of veratrin. It would seem more probable 1 , 

 therefore, that two different contraction processes are initiated by 

 the stimulus, one much more rapid than the other. Many other' 

 facts in physiology speak for this general view that a muscle may, 

 according to conditions, give either a quick contraction (twitch) 

 or a more slowly developing contraction, with a prolonged phase of 

 relaxation (tone contraction). This latter feature constitutes the 

 characteristic peculiarity of the curve of a veratrin contraction. 

 A somewhat similar effect is produced by the action of glycerin, 

 nicotine, etc. We have in such substances reagents that affect 

 one phase of the contraction process without materially influenc- 

 ing the other. As regards the veratrin effect, it becomes less and 

 less marked if the muscle is made to give repeated contractions, 

 but reappears after a suitable period of rest. The peculiar action 

 of the veratrin is, therefore, antagonized seemingly by the chemkial 

 products formed during contraction. 



Contracture. The jgrolqnged relaxation that is so character- 

 istic of the veratrimzed muscles may be observed in frog's muscle 

 under other circumstances, and is described usually as a con- 

 dition of contracture. By Contracture we mean a state of main- 

 tained contraction or, looking at it from the other point of view, 

 ii state of retarded relaxation. 



This condition is often exhibited in a most interesting way when a muscle 

 is repeatedly stimulated. In some cases it develops at the beginning of a 

 series of contractions, as is represented in Fig. 14, which pictures the phenome- 

 non as it was first described.! In other cases it appears later on in the curve, 



* "Journal de la physiol. et de la path, generale," 1899. 

 fTiegel, "Pfliiger's Archiv fur die gesammte Physiologic," etc., 13, 71, 

 1876. 



