554 



RODS AND CONES OF 



[sect. 226. 



0"0002 



point the rod is continued by an extremely delicate filament, 



thick, which becomes connected with the 

 other elements of the retina in the 

 manner to be afterwards described. 

 — The substance of the rods is clear, 

 homogeneous, with a slightly fatty 

 lustre, very soft and pliant, but at 

 the same time very brittle, so that 

 it is only in perfectly fresh eyes that 

 their true length can be recognised. 

 Their delicacy is so great, that they 

 undergo the most diverse alterations 

 even in water, and become very 

 difficult of recognition, curving into 

 the form of hooks, rolling them- 

 selves up or becoming twisted, 

 breaking into two or more pieces, 

 and effusing clear drops, which are 

 often found in enormous numbers 

 upon the outer side of the retina, 

 partly coming from the rods, partly 

 from the ruptured pigment-cells of 

 the choroid. One of the most usual 

 alterations is, that the point, when 

 it does not fall off, as is frequently 

 the case, assumes an inflated varicose 

 shape, becoming lancet-shaped, or 

 even transformed into a globule, 

 to which the filament is still attach- 

 ed ; to this is frequently superadded 

 a hook-like curve, or a slight swel- 

 ling of the obtuse extremity of the 

 rods. The rods are almost invariably 

 much altered by re-agents, especially 

 the rods themselves, which, not- 

 Avithstanding their greater breadth, 

 offer less resistance than the filaments. Ether and alcohol cause 

 them to shrivel up, and render them scarcely recognisable, but 

 they are not soluble either in these re-agents or in boiling water. 

 In acetic acid of 10 per cent, they shorten instantaneously to a 

 great degree, become distended at several places, and break up 

 into transparent globules, which resist at first, but disappear after 



Elements of the baeillar layer in connec- 

 tion with the fibres of Miilli r. From the 

 human retina, magnified 3-iO times. 1. 

 cones, with fibres of Muller; a. thicker 

 part of the cone, or proper cone ; b. rods 

 upon the same, one longer than the other ; 



c. circular line at the inner end of the 

 cone; d. nucleated swelling (cell-body) of 

 the same already in the outer granular 

 layer; e. fibre of MiiUer, into which it is 

 continued; e . lateral process from one of 

 these fibres, passing inwards; /. granule 

 (cell) of the inner granular layer ; g. inter- 

 nal termination of the fibre of Midler. 2. 

 rods with Mtillerian fibres ; a. rod ; b. 

 transverse line at its inner extremity ; c. 

 commencement of the filament of Midler ; 



d. granules of the outer granular layer, 

 one seated close to the rod ; e. fibres of 

 Miilb r in the intermediate granular layer ; 

 /. inner granules ; f. one of them with a 

 lateral process ; g. internal extremities of 

 the fibres of Midler. 3. an inner granule, 

 «, with three processes, of which the ex- 

 ternal one gives off branches, and supports 

 several other granules, 6, together with 

 rods, of which only one is figured. 





