CONTRACTILE FORCE OF MUSCLES. 215 



been shown by Mr. Bowman, however, that the stiffening of the muscles 

 after death is due to the permanent contraction of their component fibres, 

 and that the coagulation of the blood can have nothing to do with it. 

 Nevertheless, this contraction may be considered as being, for the mus- 

 cular fibre, a phenomenon of very much the same kind as the coagula- 

 tion of the fluid fibrine of the blood, especially resembling the subse- 

 quent contraction of the clot, which takes place gradually, within a few 

 hours after its separation. The causes which prevent the coagulation 

 of the blood after death ( 187), usually prevent also this last manifes- 

 tation of the tonicity of the muscles ; their vitality being completely de- 

 stroyed, like that of the blood, by sudden and powerful shocks operating 

 on the nervous system, or by the complete exhaustion consequent upon 

 violent and long-continued exertion, as when animals are run to death. 

 And again, the tonicity of muscles survives the freezing process ; mani- 

 festing itself by contraction and rigidity, in a muscle that has been 

 frozen immediately after death, and is subseqently thawed ; just as the 

 peculiar properties of the fibrine of the blood cause its coagulation upon 

 being thawed, if it have been frozen immediately upon being drawn 

 from the vessels. 



370. The power by which the elements of Muscular fibre are caused 

 to approach ' one another in . the exercise of their Contractility, differs 

 from any other with which we are acquainted. Its complete dependence 

 upon the life of the tissue is remarkably shown by the fact (ascertained 

 by Valentin), that, after the cessation of the irritability, the muscles 

 tear with a far less weight, than they were previously able to draw, when 

 excited by galvanism ; so that their contractile force is much greater than 

 that, which the simple cohesiveness of the tissue can sustain. More- 

 Over, it has been shown by the experiments of Schwann, that the con- 

 tractile force is greatest, when the muscle is most extended ; so that, 

 with the same stimulus, it can overcome a greater resistance by its con- 

 traction, when it has been previously stretched to its full length, than it 

 can when it has been already in part shortened by the exercise of its 

 contractile force. The'power diminishes progressively with the further 

 shortening of the muscle ; until at last no further contraction can be 

 produced by any stimulus, the extreme limit having been reached. 

 Hence it seems as if the contractile force of Muscles differs completely 

 from other forms of Attraction, as those of Gravitation, Electricity, &c. ; 

 since it is the universal law of their operation, that the force increases, 

 in proportion to the decrease between the squares of the distances be- 

 tween the attracting bodies ; whilst, in the case ; of muscle, the force de- 

 creases, in proportion as the distance between the attracting particles 

 decreases. But it is to be remembered that the law of attraction just 

 quoted supposes the particles to be quite free to approach one another ; 

 and this they obviously are not in the contraction of a muscle, since the 

 approach cannot take place without a change of place between the solid 

 and fluid elements ( 354). Hence it is difficult, if not impossible^ to 

 discover the law, which shall truly express the nature of the attraction 

 between the ultimate particles of Muscle at different distances ; but tt 

 law discovered by Schwann expresses the force actually developed, at 

 the different states of muscular contraction. 



