SCHULTZE, ON THE RETINA. 23 
exist cannot be doubted by any one who regards the unequal 
distribution of the two elements in different parts of the 
human retina, and remembers that in the most sensitive 
part of it, as is well known, “cones” only exist, whilst in 
every other part the “‘ rods” far exceed the “ cones”? in 
number. But these conditions have hitherto remained un- 
explained, as has also the remarkable fact that in the retina 
of many animals the “rods” alone are found, and in others 
only ‘‘ cones.” In the prosecution of his object, therefore, 
M. Schultze has found it necessary to examine, not only the 
human retina in its various regions, and particularly in the 
macula lutea and fovea centralis, but also to investigate all 
the varieties of structure exhibited in other animals. And in 
order to leave no means untried for arriving at a satisfactory 
elucidation of the subject, he has further closely studied the 
development of the retina, and particularly that of the bacillary 
layer. 
The first section of the paper is devoted to the considera- 
tion mainly of the bacillary layer in the human subject, whose 
general structure is described much in the usualterms. The 
observations were made upon the recent human retina pre- 
pared with dilute osmic acid, and the beautiful illustrative 
figures are stated to have been taken from nature. They are 
excellently done, and doubtless accurately represent the 
structure as thus prepared. Retinas hardened by immersion 
in solutions of osmic acid containing 4— 4, per cent. are 
readily split up by means of needles into their lamine parallel 
with the radial fibres ; and these products of natural fissure 
are clearly, the author thinks, preferable to thin sections. 
The principal pomts to which we shall refer, contained in 
this section, are :—(1) The fine longitudinal striation observ- 
able in the “cones” and “cone-filaments.” (2) That the 
space between the “‘ cone-filaments,” as they cross the outer 
granule-layer, is entirely occupied by small, closely crowded 
cells, all of which are connected by finer or coarser filaments 
with the “rods.” ‘These cells may be regarded, with H. 
Miiller,as bipolar ganglion-cells. (3) The distinctive character- 
isties of ‘* cone-filaments,’’ which are much thicker than those 
of the “ rods,” are then detailed, and the differences between 
them and the fibrous radial trabecule pointed out. 
The relations of the “rods” and “ cones,” and the dispo- 
sition of their filaments in the neighbourhood of and in the 
macula lutea, are next described, and particular pains are 
taken to render the structure of the retina in the macula and 
fovea centralis clear and intelligible, and, as it atin to us, 
with complete success. 
