588 MOTION. 



tlie muscular tissue of the heart, that the cessation of the 

 action of this organ in asphyxia is in some measure due 

 (p. 231). 



Besides the property of contractility, the muscles, espe- 

 cially the striated or those of animal life, possess sensibility 

 by means of the sensitive nerve-fibres distributed to them. 

 The amount of common sensibility in muscles is not great ; 

 for they may be cut or pricked without giving rise to 

 severe pain, at least in their healthy condition. But they 

 have a peculiar sensibility, or at least a peculiar modifi- 

 cation of common sensibility, which is shown in that their 

 nerves can communicate to the mind an accurate knowledge 

 of their states and positions when in action. By this sensi- 

 bility, we are not only made conscious of the morbid sensa- 

 tions of fatigue and cramp in muscles, but acquire, through 

 muscular action, a knowledge of the distance of bodies and 

 their relation to each other, and are enabled to estimate and 

 compare their weight and resistance by the effort of which 

 we are conscious in measuring, moving, or raising them. 

 Except with such knowledge of the position and state of 

 each muscle, we could not tell how or when to move it for 

 any required action ; nor without such a sensation of effort 

 could we maintain the muscles in contraction for any pro- 

 longed exertion. 



The mode of contraction in the transversely-striated mus- 

 cular tissue, has been much disputed. The most probable 

 account, which has been especially illustrated by Mr. 

 Bowman, is that the contraction is effected by an approxi- 

 mation of the constituent parts of the fibrils, which, at the 

 instant of contraction, without any alteration in their 

 general direction, become closer, flatter, and wider ; a con- 

 dition which is rendered evident by the approximation of 

 the transverse striae seen on the surface of the fasciculus, 

 and by its increased breadth and thickness. The appear- 

 ance of the zigzag lines into which it was supposed the 

 fibres are thrown in contraction, is due to the relaxation of 



