128 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



excitation by prolonged contractions. If a muscle be excited by frequent 

 induction shocks, oven at a rate insufficient to produce tetanus, after a time 

 it will take on a condition of continuous contraction, which may be main- 

 tained for sonic time after the excitations have ceased (see Fig. 50). If the 

 muscle be very irritable, the contraction caused by a single irritation may be 

 long drawn out. A muscle poisoned by veratria — and the same is true of 

 some other drugs (see p. 137) — may show a remarkable degree of contracture 

 as a result of a single excitation. The contractions of fatigued muscles tend 

 to be greatly prolonged ; and this is very markedly the case with a dying 

 muscle, which gives well-defined, long-continued contractions, localized at 

 the point excited, called by Schiff the " idio-muscular contraction." The 

 contractions caused by the making and breaking of a strong battery current 

 applied to a muscle may likewise be followed by localized contractions which 

 last a considerable time. 



In this connection one must bear in mind that the length of muscles 

 varies with their elasticity (see p. 105), and that this changes not a little 

 under varying conditions. Finally, it is necessary to recall that muscles when 

 entering into rigor mortis or rigor caloris take on a condition of contraction 

 which may last for days (see p. 159). 



Contracture in Normal Muscles following Frequent Excitations. — The con- 

 dition of prolonged after-contraction which results from frequent excitations 

 was first studied with care on the muscles of the frog, by Tiegel, 1 who gave 

 it the name of " contracture." 



Richet found that the claw-muscles of the crab are particularly subject to 

 this form of contraction, Rossbach observed it in the muscles of the cat, and 

 Mosso 2 saw it in the muscles of man when vigorously excited either volun- 

 tarily or electrically. Mosso finds a teleological reason for its existence in 

 that it appears most marked under conditions when prolonged contractions 

 are desirable, and might offer a certain economy in the innervation of muscle 

 l>\ lessening the work of the nerve-cell. Richet 3 writes that normal con- 

 tracture is not to be confused with the prolonged relaxation of fatigued and 

 dving muscles, nor with the contraction of muscle substance in rigor mortis ; 

 it is best seen on muscles which are fresh and excitable. Although most 

 readily called out by strong direct electrical excitation of the muscle, it is 

 not due to the effect of the current as such, because it may be produced by 

 exciting the muscle indirectly through its nerve, and by voluntary muscular 

 contractions of man. On the other hand, the presence of the nerve is not 

 essential, for curarized muscles may exhibit contracture. 



That a condition of increased excitability is favorable to the development 

 of contracture is made evident by the curve reproduced in Figure 57. In this 

 experiment the muscle was subjected to a tetanizing induction current for 

 nine seconds, the stimulation being interrupted for an instant every two 



1 Tiegel : PfHiget^a Archiv, 1876, xiii. S. 71-84. 



J Mosso: Archives itcdiennea de Biolorjie, 1890, xiii. pp. 165-179. 



s Richet: Dictionnairc de Physinlogie, 1899, t. iv. pp. 391-393. 



