i GENEKAL PHYSIOLOGY OF MUSCLE 5 



total length. Yet the muscle reacts by a twitch if it is stimulated 

 by pinching it with forceps at a point at which there are no nerve 

 fibres. 



Another sound argument for the autonomous excitability of 

 muscle is the so-called idio- muscular contraction observed by 

 Schiff. This is seen in fatigued or degenerating muscle, in which 

 conductivity is lowered. On stroking the exposed muscle obliquely 

 to the direction of its fibres with a blunt object, or tapping it 

 with a scalpel, a ridge of contraction appears at the point of 

 contact. This is obviously a local muscular reaction, independent 

 of the nerve. 



These direct arguments for the independent excitability of 

 voluntary muscles are confirmed by observations which demonstrate 

 the automatic and reflex excitability of involuntary muscle fibres. 

 (See Vol. I. pp. 305-12.) j 



Muscular excitability, independent of the nerves, is controlled 

 by the circulation which supplies the muscle with the nutrient 

 material and oxygen indispensable to its metabolism, and removes 

 the waste products as fast as these accumulate. Nicolas Stensen 

 (1687) first observed that after tying the abdominal aorta in 

 mammals paralysis of the posterior limbs rapidly set in, and dis- 

 appeared again if the artery were reopened after a short period. 

 In this experiment, however, the paralysis depends not only on the 

 fall of muscular excitability, but also on the anaemia of the lumbar 

 cord which is supplied by the aorta (Schiffer). If instead of the 

 aorta the iliac and crural arteries of one limb are tied, the ex- 

 citability of the muscles cut off from the circulation survives for 

 many hours (Brown - Sequard) ; as the vitality of the muscle 

 diminishes it shortens, and finally becomes rigid (rigor mortis). 

 If the circulation is re-established before the onset of complete 

 rigor, the excitability of the muscles may be recovered. 



Brown-Sequard demonstrated by a long series of experiments 

 that, after death, excitability persists for a longer or shorter time 

 in different muscles of the same animal ; that, generally speaking, 

 it survives longer if the external temperature is low, although the 

 contrary has been affirmed ; and that the longer the muscles pre- 

 serve their excitability after death, the longer are they capable 

 of recovering it on the artificial circulation of arterial blood. 



Claude Bernard stated that during muscular contraction in 

 the living animal the blood flowing away from the muscles is 

 highly venous. Ludwig further observed that during tetanisation 

 of the muscles of any limb, by stimulation of its nerves, the flow 

 of blood from the muscle was accelerated, owing to the active 

 dilatation of the vessels. Chauveau noted an acceleration of the 

 circulation in the masticator muscles of calves during mastication, 

 which was due not only to nervous influence but also to the active 

 dilatation of the muscular vessels, and to the impetus given to the 



