426 GENEKAL ANATOMY. 



cles, the serous membrane of the abdomen, &c. ; 6. Lastly, 

 the direct irritation of the muscle itself: it remains doubtful, 

 in this case, whether the exciting cause acts immediately on 

 the muscular fibre, or through the medium of the nerves. 

 What renders this last supposition the more probable, is that 

 the irritation of a part of a muscle produces the contraction of 

 the entire muscle itself. 



682. The, cause of muscular action is, like that of all or- 

 ganic action, almost impossible to'determine: we know the 

 phenomena and conditions, beyond that, all is mere hy- 

 pothesis. This cause has been ascribed to the action of the 

 nerve, to that of the blood, to the reciprocal action of the 

 nerve and the blood in the muscle; and according to the doc- 

 trines prevailing at different periods, these opinions have given 

 birth to a great many different hypotheses, none of them have 

 accounted for the augmentation of the power of cohesion of the 

 muscle. . It is evident that during contraction there is a mo- 

 mentary increase of molicular attraction between the particles 

 of the fibre. If the plaited form assumed by the fibre be con- 

 sidered, as well as the connexion of the nervous filaments with 

 their plaits, it may readily be conceived that the nervous in- 

 fluence must share largely in the phenomenon of contraction. 



683. Is irritability a power inherent in the fibrinous sub- 

 stance of the muscle, and does the nervous action only there 

 take place like any other excitant causing contraction? In this 

 hypothesis, the nerves would, in the voluntary muscles, only 

 fulfil the function of irritating .them; and with respect to the 

 muscles which, as the heart, do not contract voluntarily, 

 the nervous- action would not manifest itself under ordinary 

 circumstances. Or, on the other hand, has irritability its only 

 source in the nervous system? By this hypothesis, the nerves 

 would fulfil, with regard to the voluntary muscles, the double 

 office of rendering them irritable and of causing them to con- 

 tract; and, with regard to the involuntary muscles, the con- 

 traction of which is determined by local stimulants, it would 

 render them' only predisposed to this contraction. Or, lastly, 

 have the muscles an inherent power, (visinsita) and a power 

 borrowed from the nervous action (vis nervea)? It is almost 



