GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 129 



seconds, to permit the contracture which was present at these times to show 

 itself. The effect was to increase the excitability of the muscle, as shown 

 by the increased height of the contractions recorded after the tetanus, and to 

 produce a marked contracture, as was shown by the fact that the muscle only 

 partially relaxed after the tetanizing current had ceased, and kept partially 

 contracted in the intervals betweeu the succeeding separate contractions. The 

 fact that contracture can develop hand in hand with increasing excitability 

 shows that it may occur in the absence of fatigue. It is interesting to note 

 that the muscle made contraction and relaxation movements at the same 

 time that it remained continually, although incompletely, contracted ; and 

 finally, that the contracture offered a firm, elastic support to the separate 

 contraction movements, and that the relaxation movements following these 

 separate contractions were rapid, as is made evident by the character of the 

 elastic oscillations resulting from the rapid fall of the lever. 



The fact that a muscle can remain continuously, though incompletely, con- 

 tracted, at the same time that it makes rapid contraction and relaxation move- 

 ments, suggests that it may at the same time be the seat of two independent 

 contraction processes. The observation recalls the action of the heart mus- 

 cle, for the ventricle maintains a condition of greater or less tonus, at the 

 same time that it makes separate beats ; it is therefore in harmony with a 

 well-known physiological process. 



Contracture following Single Excitations. — An examination of the contract- 

 ure effects sometimes seen to follow single excitations of irritable muscles 

 throws some light on the nature of the process. Richet observed on the 

 closing-muscle of the claw of the crab that a single excitation caused a rapid 

 contraction, which was followed by a rapid relaxation, and this in turn by a 

 second contraction movement which lasted a considerable time. 



A similar curve maybe obtained from the striated muscle of a frog incom- 

 pletely poisoned with veratria ; if a single shock be given, the curve rises 

 suddenly, and this quick rise is followed by an immediate fall, which is inter- 

 rupted by a second and slower rise, which is continued as a prolonged con- 

 traction. In both cases the curve suggests thai the single excitation called 

 out two contraction movements, the first a rapid, short-lived contraction, the 

 second a slower, prolonged contraction. It has been suggested that the mus- 

 cle contains two kinds of muscle-fibres, which, like the pale (rapidly con- 

 tracting radialis externus) and red (slowly contracting radialis interims) 

 muscles of the rabbit, have two different rates of contraction. 1 This expla- 

 nation is not very satisfactory, because it has been (bund that both the pale 

 and the red muscles of the rabbit can give typical veratria contracture curves. 1 

 Moreover, both heart-muscle and non-striated muscles show independent tonus 

 and contraction movements though containing only one kind of muscle-fibre. 3 



1 Grutzncr: Pfluget>6 Archiv, 1887, Bd. 41, S. 256. 



2 ( 'iirvallo and Weiss: Journal </< I'lii/siolonif ft I'atholoyie ijenerale, 1899, t. i. p. 1. Bu- 

 cannan : Journal of Physiology, 1899, vol. xxv. p. 145. 



3 Jiottazzi : Journal of Physiology, 1897, vol. \xi. p. 1 



Vol. II.— 9 



