CLARKE, ON NERVE-FIBRE. 67 



Lister and Turner inspected, and made the subject of com- 

 ment in the last number of this journal. It is true, that in 

 the transverse sections the spiral arrangement around the 

 axis-cylinders is frequently, but not always, very faint, in 

 consequence, I think, of the aqueous solution of carmine in 

 which they are immersed, and which probably allows the 

 turpentine to have a greater influence on the white substance ; 

 for in the ?m-coloured preparations, when properly made, the 

 spirals, or concentric circles, are most distinctly marked, and 

 their outlines, as well as the intervening connective tissue, 

 are more sharply defined than in any sections of the medulla 

 simply hardened in chromic acid. Preparations of this kind 

 are in the possession of several eminent physiologists, amongst 

 whom I may mention Professor Hughes Bennett, of Edin- 

 burgh ; so that Messrs. Lister and Turner will have the 

 opportunity of inspecting them. While the white substance 

 of Schwann, however, is thus distinctly observable in trans- 

 verse sections, it is often but faintly seen, and sometimes 

 invisible, in longitudinal sections, unless the medulla be 

 hardened in a peculiar way, by first using a weak, and then 

 a very strong solution of chromic acid. But even the total 

 loss of this substance Avould be of little or no importance in 

 tracing the course of the fibres and their relation to other 

 tissues, for their axis-cylinders are rendered more than 

 naturally conspicuous and strong j while their sharpness of 

 outline, the fine definition of the other tissues under high 

 powers, and the advantage of examining them in sections of 

 amazing thickness, fully compensate for a loss which mav 

 easily be supplied, when necessary, by some other mode of 

 preparation. But, as already stated, whenever we wish to 

 ascertain the natural appearance and structure of the nerve- 

 tissues, we must abstain from all kind of preparation. Before 

 I proceed further, however, I will briefly explain the doc- 

 trines of Stilling on the structure of nerve-fibre. 



In 1855, Stilling announced to the Academy of Sciences of 

 Paris, as the results of his inquiries, that the whole of the 

 primitive nerve-fibre — the membranous sheath, the white 

 substance of Schwann, and the axis- cylinder — are composed 

 of a continuous network of similar " elementary tubules."* 



* ' Comptes Reudus. 5 He also states that the finest branches into which 

 the processes of the nerve-cells divide, resemble the "elementary tubules" 

 of the primitive fibres, and that the cells are connected with each 

 other by their processes (p. 899). In the same volume (p. 956), M. 

 Gratiolet informs the Academy that he described this anastomosis of 1 he 

 cell-processes as early as 1852. M. Gratiolet was evidently not aware 



