32 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



to conditions, give either a quick contraction (twitch) or a more 

 slowly developing contraction, with a prolonged phase of relaxa- 

 tion (tone contraction). This latter feature constitutes the char- 

 acteristic pecuharity of the curve of a veratrin contraction. A 

 somewhat similar effect is produced by the action of glycerin, 



Fig. 13. — Curve showing the effect of veratrin. 



nicotin, etc. 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 chemical 

 products formed during contraction. An apparently similar 

 phenomenon is exhibited in the disease known as myotonia con- 

 genita or Thomsen's disease. When an individual thus afflicted 

 makes a voluntary movement the contracted muscles relax with 

 abnormal slowness, so that the muscle remains in a condition of 

 cramp or tonic spasm. With repeated use, as in the case of the 

 veratrinized muscle, this condition disappears and the movements 

 become normal. 



Contracture. — The prolonged relaxation that is so character- 

 istic of the veratrinized 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, 

 a 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, 

 preceding or following the development of the state of fatigue. Whenever 

 it occurs the effect is to hold the muscle in a state of maintained contraction or 

 tone, on which is superposed the series of quick contractions and relaxations 

 due to the separate stimuli. When the condition develops early in the func- 

 tional activity of the muscle (Fig. 14) further activity usually causes it to dis- 

 appear, and the condition of the muscle as a mechanism for prompt shortening 

 and relaxation is improved. When the contraction appears late in the series of 

 contractions it is usually permanent, that is to say, it wears off only as the 



* Tiegel, "Ffluger's Archiv fur die gesammte Physiologie," etc., 13, 71, 

 1876. 



