On the Minute Structure of Striped Muscle, fyc. 297 



the relative quantities of fluid held by the substances producing the 

 striping. Inasmuch, however, as the changes in the striping are 

 due to changes in form of the fibrils, the very foundation of these 

 theories has been removed. 



The Author's Views as to the Structure of Striped Muscle. 



Before proceeding further I would venture to state what I think 

 we are in a position to affirm respecting the structure of striped 

 muscle. The fibres consist of fibrils generally grouped together in 

 bundles and separated from each other by interfibrillar matter. As 

 tho fibrils are varicose, and have a different refractive index from the 

 interfibrillar matter in which they lie. they, in consequence, present 

 the optical striping possessed by all such bodies under similar circum- 

 stances, and we have no reason to suppose that this striping has any 

 other interpretation. The fibrils, from whatever point we look upon 

 them, are composite structures, and their varicosity indicates this 

 quite clearly. Each fibril has practically undergone segmentation 

 into a series of tiny particles, although there is no evidence that these 

 are separated from one another by membranes, or any other anatomical 

 structures, and each little bit contracts on its own account so as to 

 thicken and shorten. Although we know absolutely nothing as to 

 what there is within each fibril, yet the condition of parts, whatever 

 it may be, is probably the same in every Dobie's line, or in every dim 

 or light stripe. Each light stripe may merely consist of contractile 

 tissue in a different state of tension from that in the position of the 

 dim stripes, and if so, that may partly interpret the polariscopic 

 phenomena, but beyond the fact that a difference exists we are not 

 in a position to make a further affirmation. When we study the 

 change in form which these little segments undergo in passing from 

 the relaxed into the contracted condition we come upon several 

 curious facts, the interpretation of which is at present very difficult. 

 Some muscles, and especially those of some of the lower Vertebrates 

 appear to be very simple in form, and to undergo very simple changes 

 during contraction. I hope to enter into greater detail in a subse- 

 quent paper, but in the meanwhile I would simply state that the 

 fibrils seem to be devoid of the tiny swellings which form the line of 

 Dobie. The fibrils, therefore, possess simply alternate swellings (dim 

 stripes) and constrictions (clear stripes). During contraction, the 

 swellings become more marked as the fibrils shorten, the change 

 being represented in fig. 2. 



In this case the dark stripes of the contracted fibre are at just the 

 same parts of the fibril as in the relaxed condition. In other 

 in most of the Arthropoda, for instance, the stripes are 

 ersed, as already so well described by the German histologists. 



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