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Mr. J. B. Haycraft. Upon the Cause of [Feb. 3, 



the substance of the clear stripe, which he considers as fluid " Muskel- 

 kastckenflussigkeit,'' passes between the little elements of the dark 

 stripe, causing their lateral separation, and therefore broadening 

 and shortening the fibre. Engelmann ("N"eue Untersuckungen uber 

 die Microskopischen Yorgange bei der Muskelcontraction," in 

 " Pfluger's Archiv," Bandxviii) is certain that the light stripe during 

 complete contraction becomes darker than the dark stripe, and that 

 there is a period as naturally follows from this observation, when 

 the fibre is quite unstriated. The stripes are in fact reversed, the bright 

 one becoming the darker, and vice versa. Both stripes narrow, but 

 especially the bright one. Engelmann advances a theory to account 

 for this, holding that the cause of contraction is the passage of fluid 

 from the isotropous clear stripe into the anisotropous substance ; the 

 former shrinks, and the latter swells. Most startling is the view of 

 Merkel (" Hofmann und Schwalbe," vol, i, p. 116), who believes that 

 the dark stripe shifts its position, arranging itself by Dobie's line, 

 while the light stripe passes to the centre. 



It is, as will readily be admitted, somewhat difficult to know what 

 to believe, for there is such entire disagreement among physiologists 

 as to simple facts, to say nothing of any conclusions which may be 

 drawn from them. Thinking that there must be some simple clue 

 which would solve the whole problem, I commenced to work at the 

 subject in the summer of 1878. At the onset the clue was discovered, 

 and the substance of the present paper was written by the end of that 

 year, before I had read for the first time the paper of Mr. Bow- 

 man's, in the " Transactions " of this Society. My astonishment 

 was indeed great to find in it the first glimmerings of my own 

 opinions, for although the subject had then been worked out but in 

 the rough, and Mr. Bowman had a much simpler problem to deal with, 

 yet undoubtedly he held the same views in the main. My obvious 

 course was therefore entirely to re-write my paper, making every 

 acknowledgment to his already published work. He considered, 

 as far as I can make out, that the light stripe was to be compared 

 with the cement seen in longitudinal fibrillation, between the fibrillee, 

 yet he looked upon the strias as being due to the shape of the fibre. 

 From the history of the subject, which has just been given, it will be 

 seen that all observers are not agreed as to the actual appearances of 

 a striped fibre, and especially the changes which occur during contrac- 

 tion, and I hold that they have fallen into great and unwarrantable 

 error in the conclusions (these, indeed, are all contradictory) drawn 

 from these appearances. A fibre has been observed in the field of the 

 microscope, which is marked transversely, as already described, and 

 all modern investigators have concluded that the transverse bands 

 mark the positions of disks (seen on edge) of tissue of different refrac- 

 tive indices and chemical composition, alternating in the long axis of 



