Dr. .1. I'.. Ih.vrrafr. 



Fio 2. 



& a 



FIG. 3. 

 Jf C 



fl 







I'm. '2 (R) represents a relaxed fibril with a pin, A 

 During its contraction (C), as the fibril simply 

 otherwise changing its shape, the needle A is 

 stripe. 



FIG. 3 (R) represents n relaxed fibril with a pin, A, 

 and another pin, S, sticking into the swelling 

 When contracting (O), the fibril is profoundly 

 sticking into the clear stripe, and the pin R into 



, sticking into the dark strij 

 shortens and thickens withe 

 still seen sticking in the dai 



, sticking into the dark strij 



in the position of Dobie's lin 



modified in shape, the pin 



the centre of the dark stripe. 





The reason is that, during contraction, the fibrils change thei 

 shape in such a manner that the parts which previously bulged no 

 become the thinnest part (fig. 3). As the fibrils begin to cout 

 the substance of the clear stripe becomes an eminence ins 

 of a depression, and the little bulging part forming Dobie's li 

 becomes smoothed out and gradually obliterated. The dark stri 

 on the other hand, becomes the constriction in the case of tl 

 contracted fibre, and, of course, appears now as a clear band. These 

 points can only clearly be made out by studying all the int 

 mediate conditions between complete contraction and relaxation, 

 they are best seen in the living muscle fibres on which waves 

 contraction are still slowly passing ; one may see them, too, upon the 

 muscle impressions. I have never happened to make an impression 

 of a fibre showing a series of these intermediate stages in a short 

 piece of a fibre while engaged with Dr. Edington in photographing 

 them, but fig. 4 shows very well the appearance ; it is a careful 

 drawing of a Crab's muscle in a state of contraction, but bent at an 

 angle so that the convex side is artificially extended. The Dobie'ft 

 lines on the extended side are seen gradually to thin away, and 

 gradually disappear on the contracted side, while the surrounding 

 bands which appear as clear depressions gradually become dim 

 elevations. 



Of course, this change of form leads to the shortening of the fibrils, 

 but it is at present difficult to say why this reversal of the vari 

 should occur ; at present, we have to accept it as an unexplained fact. 



