CONTRACTILITY. 717 



or of the stiffening of limbs after death,) he From these different modes of excitation of 



gives this name to contractions which are the contractile power of muscular parts, diffe- 



strictly vital. Almost all animal substances rent names have been given to the power 



are liable to contraction from heat, and from itself, as by Haller, who applied the term 



the application of various chemical agents Vis Tonica to the contraction from distension, 



which affect them as astringents, to which Vis Insita to the contraction from irritation of 



property Bichat gave the name of Contractilite the muscular fibres themselves, Vis Nervosa to 



par racornissement ; and it is easy to perceive the contraction from irritation of a nerve, and 



that this property also, although persistent in Vis Animalis to the contraction from volition, 



the perfectly dead body, and therefore inde- acting at the brain and transmitted through a 



pendent of life, may give occasion to contrac- nerve ; or again by Bichat, who applied the 



tions which may sometimes be mistaken for term Contractilite Organique Sensible to the 



indications of the strictly vital contractility. contractions excited by any kind of irritation, 



Confining our attention, however, to such acting on muscular fibres themselves, and the 



contractions of the solids of organized bodies, term Contractilite Animale to those excited by 



as are exhibited by them only in their living stimuli, whether mental or physical, acting on 



state, i.e. so long as they present that assem- the nerves, spinal cord, or brain. But it is 



blage of phenomena, to which we give the obviously more correct to distinguish the dif- 



name of Life, we proceed to state the facts ferent varieties of the vital power according to 



which seem to be most important and best the phenomena, which the contracting part 



ascertained, first, as to the modes in which presents, than according to the manner in 



they are excited ; secondly, as to their pheno- which the contractions are excited ; and there- 



mena, and varieties; thirdly, as to the condi- fore those terms have fallen much into disuse, 



tions necessary to their manifestation ; and, In most instances, it is the same vital power of 



lastly, as to the laws which regulate them. Irritability, as above defined, which is called 



I. It is universally known, that the most i llto action in these different ways. 

 striking examples of vital contractions are seen It is only of late years, that it has been 

 in the effects produced by various stimuli fully ascertained, as to the excitement of vital 

 acting on muscles, particularly those of volun- contractions through nerves : 1, that it is, almost 

 tary motion, and the heart. The essential cha- exclusively, in the case of muscles which are 

 racters of muscular fibres, their composition naturally subject to the Will, that even physical 

 nearly akin to the fibrin of the blood, their irritation, confined to the nerves, has power 

 arrangement in parallel fasciculi, which are to excite contraction; and 2, that these muscles 

 bound together by cellular membrane, their nav e nerves, or nervous filaments, from two 

 soft texture, and slight elasticity are also ge- distinct sources, viz. from the anterior and 

 nerally known. The change excited by sti- posterior columns of the spinal cord, and their 

 muli acting on them is a contraction in the prolongations within the cranium; and that 

 direction of the visible fibres of the muscle, it is by irritation of the first of these only, 

 which in the healthy state always rapidly (or almost exclusively,) that the muscular con- 

 alternates with relaxation; and by these two tractions are excited.* From these facts, it 

 circumstances, the excitation by stimulus, appears obvious, that the grand and eternal 

 and the quickly ensuing relaxation, we dis- law of separation, as Haller calls it, oftheVo- 

 tinguish that form of Vital Contractility, to luntary and Involuntary muscles, consists essen- 

 which the term Irritability is most correctly tially, not in different powers of the muscular 

 applied. parts, but in different endowments of the ner- 



The stimuli which produce this effect are vou s filaments which enter them, 

 very various; and the experience of our own In regard to the excitation of muscular con- 

 bodies points out the obvious distinction of traction through nerves, it is also to be ob- 

 these into physical and mental. Of the first served, that although the action of muscles in 

 kind, air and water, especially if aided by heat, obedience to the will is the most obvious and 

 act decidedly in this way; but those which striking example, in the living body, where 

 have been chiefly used in experiments are, dis- the intervention of a change in a nerve is known 

 tension, especially in the case of the hollow to be an essential condition of the act, yet 

 muscles, such as the heart or bladder, che- there are many examples of movements, per- 

 mical acrids, such as acids, alkalies, various formed by voluntary muscles, in obedience to 

 alkaline, earthy, or metallic salts, and elec- mental stimuli, but not to volitions, to sensa- 

 tricity or galvanism. The effect of all these tions, or other involuntary acts of mind, even 

 stimuli is much increased by their being sud- in opposition to efforts of the will. These con- 

 denly applied. stitute a very important class of vital motions, 



It has also been long known, that many and are known to be equally excited through 

 muscles are excited to contraction by such sti- the motor nerves of the muscles concerned in 

 muli, when applied to certain nerves, entering them. Of this kind are not only the irregular 

 their substance, or to certain parts of the spinal agitations of the limbs produced by tickling, or 

 cord or brain, even more effectually than by the convulsive writhing of Xhe body from pain, 

 applications to themselves; and likewise, that but also, such regular and admirably precise 

 it is only when those nerves are entire, up to movements as shrinking when pain is excited 

 the brain, that those muscles which are natu- 

 rally obedient to the mental stimulus of the * See Mayors Outlines, 2d edit. p. 50 ct seq. 

 Will, can be excited by voluntary efforts. and Sir C. Bell, Phil. Trans. 1826. 



