240 ANIMAL FORCES. [ii. 



(48). This reflexion of the impression can excite indirect nerve- 

 actions in all other parts of the muscle. It is difficult to decide 

 which of these two modes of action takes place, when an entire 

 muscle, or muscular viscus, is excited to movement by the 

 irritation of a single point ; but it is necessary for the sake of 

 establishing the correctness of the doctrine, that the possible 

 distinction be known. 



448. The motion of which a muscular fibril is capable, is 

 alternate cqntractiop and relaxation. According to the views 

 stated in the previous paragraph, irritation of a single fibril 

 may excite entire muscles, or bundles of fibrilli, into action, 

 and by means of the latter, entire viscera and limbs be put 

 into motion. When an impression produces this motion it is 

 animal, whether it arise from a conception, or from an irritation 

 applied to the nerves of the fibrilli (161 — 163, 193). Thus, in a 

 decapitated animal, an external impression produces contrac- 

 tions, spasms, &c., in a muscle, by a direct nerve-action, and 

 thereby puts those limbs into movement to which it is attached, 

 just as a volition would. And thus, many movements which 

 are or may be sentient actions, result from the direct nerve- 

 actions of external impressions on the muscles ; as when the 

 irritated muscle moves a limb by its contractions, or closes a 

 cavity, or, as in the intestines, causes peristaltic movements and 

 numerous writhings. 



449. Neither the mind, nor internal impressions on the 

 brain or nerves, are necessary to direct nerve-actions in the 

 muscles. They occur, although the brain be compressed, or 

 even the head removed from the body, and although the nerve 

 going to the muscle be divided, or the muscle itself excised. 

 All these are points of distinction between direct nerve-actions 

 and sentient actions generally, but especially those of external 

 sensations (164, 204). 



450. Although, therefore, after the functions of the brain are 

 arrested, or the nerve divided or tied, the muscle is excited to 

 motion neither by the cerebral force, nor by any other internal 

 impression above the point of division, but remains paralysed 

 (415, ii) to all impressions, still the nerve itself retains the 

 power of producing direct nerve-actions in it, by means of an 

 external impression. 



451. It is not every irritation that excites direct nerve- 



