284 Prof. E. A. Schafer. On the Minute Structure of the 



thin septa) of the sarcons substance through the clear interval to the 

 transverse membranes. The whole sarcostyle appears to be itse 

 enclosed by a membrane of extreme delicacy. 



If we assume, as is to all appearance the case, that the substance 

 the clear interval is of a fluid or semi-fluid nature, the above view 

 the constitution of the sarcostyle, which is illustrated with nnmi 

 takable clearness in the photographs, enables one to form a tolerabh 

 reasonable idea as to the physical change which may occur when th 

 sarcostyle passes from the condition of extension to that of retraction 

 and vice versd. For if the sarcostyle be extended, the sarcous element 

 being marrowed and laterally compressed by the extending force, th 

 fluid which is contained in their canals will become squeezed out, an 

 will pass into the clear intervals, while, at the same time, the procesi 

 of extension will elongate the sarcoas elements and separate then 

 further from the transverse membranes. With further extension, 

 separation of the sarcons element in the middle may also occur 

 some of the expressed fluid passing into the interval between the tw 

 halves.* 



On the other hand, when the extended sarcostyle becomes retracte* 

 (? contracted), the sarcous elements swell and the clear interval 

 become shortened so as eventually almost to disappear. This can onl 

 be effected by the absorption of the homogemeous substance of th 

 clear intervals into the sarcous element, and in all probability it i 

 imbibed into the canals or visible pores of the sarcous substance 

 The process may, in fact, be roughly compared with that which woul 

 occur with a series of pieces of sponge, placed at short intervals, in 

 thin- walled elastic tube filled with fluid. If the tube were extender 

 the fluid would be squeezed out of the pores of the sponge, am 

 would go to increase the volume of that in the intervals ; on relaxin 

 the extending force, the fluid would be re-imbibed by the sponge, an< 

 the intervals would be diminished. This comparison is not intend* 

 as an explanation of the mechanism of muscular contraction, bu 

 merely as an illustration of the physical changes which may reason 

 ably be supposed to accompany the varying conditions of extension o 

 the muscle. 



The subject of this preliminary communication is treated of m 

 fully in a detailed account of the structure of muscle which wil 

 shortly appear in the ' International Journal of Anatomy and Ph 

 logy.' Since, in that account, I shall have occasion to refer 



* This separation does not always occur with continued extension, for in 

 carcostyle photographed in fig. 4 the sarcous elements of the extended part, 

 although they show the effect of traction in their elongation and narrowing, are not 

 separated and contracted in the middle, as in the sarcostyle shown in fig. 3, but are 

 even slightly bulged at the centre. There appears, however, a slight tendency for 

 ll.ci.- ends to separate as (? accessory disks). 



