STRUCTURE OF NERVE FIBRES. 161 



observations, axis cylinders exist in which the original fibrillar nature 

 is entirely lost by fusion of the fibrils with each other, and which 

 have thus become homogeneous ; but I regard the principle as correct, 

 that the thicker axis cylinders are composed of several primitive fibrils, 

 since these converge at the centric, and for the most part separate from 

 one another at the peripheric extremity. On physiological grounds 

 also I maintain the possibility of isolated conduction in these con- 

 stituent fibrils, even when no trace of interfibrillar substance is 

 present. 



I may just add that my views on these points differ essentially 

 from those of Stilling,* who indeed regards the axis cylinder as a 

 complicated fibrous structure, but distributes his elementary fibrils 

 generally on the surface, and considers that they unite with consti- 

 tuents of the nerve and medulla, which also again consists, accord- 

 ing to him, of fine fibres or tubules. Stilling, as is well known, has 

 not been able to distinguish the preformed structure from the pro- 

 ducts of coagulation that occur in nerve fibres hardened in chromic 

 acid. 



Both naked axis cylinders, and those enclosed in a medullary sheath, 

 offer some remarkable and unexplained peculiarities when they are satu- 

 rated with dilute solutions of nitrate of silver in the dark, and are 

 then exposed to light. After Frommann,f who made the first ob- 

 servations on the point, the best subsequent investigations have been 

 made by Dr. Grandry.j: As a result of this treatment there occurs 

 in the axis cylinder a fine transverse striation, caused by the partial 

 deposition of brownish-black silver compounds, which is here and 

 there so regular as to remind the observer of the structure of striated 

 muscular tissue, though in other parts it exhibits great irregularity. 

 When the action of light has been more protracted, the appearance in 

 question gradually disappears, and the whole becomes equably tinted 

 of a brownish black. As Grandry remarks, however, not only the 

 axis cylinder, but also the branched processes of the ganglion cells, 

 and frequently the cells themselves, exhibit this striation in a very 

 surprising manner. No one has hitherto succeeded in showing any 

 relation between these appearances and the finer structure of the 

 parts. 



* Neue Untersuchungen uber den Bau des Itiltkenmarkes, 1859, p. 708. 

 t Virchow's Archiv, Band xxxi., Taf. 6, figs. 11 to 16. 

 | Recherches sur la Structure intime du cylindre de I'axe et des cellules 

 nerveuses, Bulletin, de I'Academie Roy ale du Belgique, Mars, 1868. 



