NERVOUS CONSTITUENTS OF THE RETINA. 225 



for the most part in their interior, a granular change of the 

 fibre-substance, whilst the parts which have not become swollen 

 by imbibition remain homogeneous, and permit the fibrillar 

 structure to be more or less distinctly recognized. That phe- 

 nomena of imbibition here play an important part is shown by 

 the behaviour of the nerve fibres of the retina in solutions of 

 chromic acid, which when sufficiently concentrated prevent the 

 formation of varicosities, whilst when rendered more and more 

 dilute the number and size of the varicosities progressively 

 increase, till at length the fibre, beset with enlargements till 



Fig. 345. 



Fig. 345. Nerve fibres of the retina, with and without varicosities. 

 a, From the Ox ; the remainder from Man. Magnified 800 diameters. 



it resembles a string of beads, altogether breaks up.* This 

 occurs in the case of the finest fibres, the varicosities of which 

 are relatively the largest from the very commencement, and 

 are in more close proximity with one another, whilst they 

 make their appearance earlier than in the thicker fibres. 



Dichotomous divisions of the nerve fibres have been de- 

 scribed and depicted by Corti-f- and Gerlach.^ These occur as 

 a rule in the optic-fibre layer, but are only exceptionally met 

 with ; the cases that have been described may possibly have 

 been instances of the bifurcation of processes of ganglion cells. 



* More precise statements in regard to the solutions in which varicosi- 

 ties occur, will be found in my Essay in the Monatsberichten der Academic 

 der Wissenschaften zu Berlin, 1856, p. 511. 



t Mliller's Archiv, 1850, Taf. vi., fig. 3. 



Handbuch, der Gewebelehre, 1854, p. 498. 



VOL. III. Q 



