2-2'2 THE EETINA, BY MAX SCHULTZE. 



medulla, which resemble the elements of the white substance of 

 the brain.* Longer portions of medullated nerve fibres may be 

 isolated by teazing out fine longitudinal sections of the optic 

 nerve preserved in hardening fluids. These also resemble the 

 medullated fibres of the white substance of the brain, when 

 subjected to similar treatment, in the circumstance of their sur- 

 face being beset with knots and varicosities.f It would there- 

 fore appear that the fibres of the optic nerve resemble those of 

 the brain in being destitute of the sheath of Schwann. The 

 superior firmness of the optic nerves to the brain substance is 

 sufficiently explained by the large amount of dense connecting 

 substance they contain, the presence of which can be demon- 

 strated in fine transverse sections of the hardened nerves. Each 

 fasciculus of nerve fibres is separated from the adjoining ones 

 by a thick layer of highly vascular fibrillar connective tissue. 

 Extremely instructive specimens may be obtained from sec- 

 tions of this kind, if taken from optic nerves which have 

 been hardened for a short time in a strong solution of per- 

 osmic acid, or, as F. E. Schulze recommends, in chloride of 

 palladium, or from fine sections otherwise hardened, coloured 

 with chloride of gold (Leber), and explain how Klebs could 

 maintain that the quantity of connective tissue in the optic 

 nerves is often still more abundant than that depicted in 

 fig. 5 of Plate xix. of the Icones physiologies. The differ- 

 ences existing between normal and atrophic optic nerves have 

 been very exactly described elsewhere by Leber, so that at 

 a rough guess the fasciculi of nerve fibres constitute about 

 one half of the mass of the optic nerve. In every fasciculus, 



* This similarity of the fibres of the optic nerves with those of the 

 brain, and their difference from other peripheric nerves, was first de- 

 scribed and illustrated with many drawings by Ehrenberg, Abhandlungcn 

 der Acad. der Wissenschaften zu Berlin aus dem Jahre, 1854, p. 665 

 T a f. i._v. 



t See this Manual, p. Ill, fig. 19. 



t See the description and illustrations of transverse and longitudinal 

 sections of these nerves given by Bonders, in Griife's Archiv, Band i. , 

 Abtheil. 2, Taf. ii., figs. 2 and 3 ; by Henle, in his Anatomic dcs Menschen, 

 Eingeweidelehre, p. 583 ; and by Leber, in Grafe's Archiv, Band xiv., ii , 

 Taf. v., fig. 1. 



Virchow's Archiv, Band xix., p. 324. 



