Plants, and on Muscle. 279 



the spiral fibre ; on the contrary, somewhat prepossessed against such 

 a theory ; for while I had already made up my mind as to the non- 

 existence of the discs advocated in I\Ir. Bowman's very ingenious 

 paper in the ' Philos. Trans./ I had not been able to bring my belief 

 to the idea of substituting a spiral thread or fibre to account for the 

 peculiar markings on the muscular fasciculi. You have, however, 

 convinced me, for in several instances I was enabled to follow the spiral 

 thread round its axis, and to see the continuitj^ of both sides of the 

 chain. In one or two instances I observed it dravi-n out or separated 

 so far as not to leave a doubt of its reality. In the same way I di- 

 stinctly recognised the double spiral (especially in one preparation 

 where the two spirals had not an equal obliquity), and I can conceive 

 that the longitudinal lines or fibrillated appearance of the larger fas- 

 ciculi depends upon the even juxtaposition of many minute spirals. 



" The reason, probably, I had failed in previously making out 

 this structure, resulted from my expectation of seeing this appear- 

 ance throughout the whole length of a filament ; but I now observe 

 how minute is the care necessary to separate parts, and how small 

 often is the portion favourably situated or sufficiently isolated to ad- 

 mit of a distinct view of this curious structure. 



" Tliere are also many circumstances connected with the different 

 refrangibility of objects of great importance in explaining why a 

 spiral fibre should be so much more easily seen in one tissue than 

 another ; and thus it is that reagents are often most usefully ap- 

 pUed where different parts of the same object refract the light nearly 

 equally. I think, through your hel]), I have at last settled my belief 

 as to the true character of the markings of muscle, and for which I 

 beg you to accept the thanks of 



" Yours faithfully, 

 (Signed) " John Dalrymple." 



" To Martin Barry, M.D." 



The following, connected with the same subject, was re- 

 ceived from Dr. Carpenter, bearing the same date as his tes- 

 timonial above given. 



" I have this day had the opportunity, through Dr. Barry's kind- 

 ness, of examining several of his preparations of muscular fibre, 

 especially those from the heart of the turtle and from the shrimp. 

 I laave distinctly seen single spiral threads continuous with fasciculi ; 

 in one or two instances so little elongated as to resemble a cork- 

 screw ; in others drawn out more or less straightly. In several 

 fibrillse, which had been isolated without disturbance of their struc- 

 ture, I have seen appearances closely corresponding with those repre- 

 sented by Dr. Barr}' in figs. 52 and 56 of his last paper [Phil. Trans. 

 1842]. I may add, that I have seen these ajDpearances even more 

 distinctly under my own microscope, which is furnished with one of 

 Powell's latest 1-1 6th objectives, than under Dr. Barry's instrument, 

 in which lower powers were used. 



(Signed) " William B. Carpenter." 



The microscope I use is one of Schiek's achromatics, si- 



