214 E. A. Schäfer, 



the changes which are observed to occur in the sarcous elements in 

 the passage into the retracted condition or, which is practically the 

 same thing, the condition of contraction. 1 ) 



It does not follow that the extending force (which may be regard- 

 ed as ordinarily operating slowly) is external to the muscular fibre, 

 although an external extending force would necessarily produce the 

 same effect. For we can conceive that during the life of the muscle 

 there is, in the resting condition of the fibre, a tendency for fluid to 

 pass out from the tubular fibrils into the clear spaces next Krause's 

 membrane: this would in itself produce an extension of the muscle 

 column and of its envelope which would call the elasticity of the 

 latter into play. Such slow passage of fluid from the pores of the 

 sarcous element might be due to what, for want of a better term, we 

 may call vital forces, causing an alteration in the elastic conditions 

 and form and in the capacity of the tubules of the sarcous element 

 to retain their fluid. The effect of an excitation to contraction might 

 be supposed to produce a rapid flowing back and re-imbibition of the 

 discharged fluid. This re-imbibition would be accelerated by the 

 elastic reaction of the stretched sarcomere. 



To explain the breaking up of the sarcous elements into 

 transverse portions in the greatly extended fibre it appears neces- 

 sary further to suppose that the sarcous elements are compounded of 

 two or more disks, placed end to end, and having under ordinary cir- 

 cumstances no perceptible interval between the successive series, 



*) In using contraction and elastic retraction as synonymous terms, I am follow- 

 ing in the footsteps of many of my predecessors who have described the appearance 

 of contracted and contracting muscles as they are seen in „fixed" preparations. The 

 appearances of contraction have been usually described as „contraction- waves" or 

 „contracted parts of fibres", but it is certain that they might equally well be de- 

 scribed as ,retracted", being compared with other parts which are „extended". It 

 has, moreover, yet to be proved that the contraction of muscle is anything more 

 than elastic retraction. This idea of muscular contraction occurred to Schwann, who 

 compared an extended muscle to a stretched spiral spring and its contraction to a 

 shortening of the spring, due to a sudden alteration in its condition of elasticity. 

 Nor has Schwann's idea been forgotten or considered unworthy of adoption: on the 

 contrary, the probability of snch an explanation of the contractile phenomena has 

 been urged with much force of reason by Eichet and other writers on the physiology 

 of muscle. 



