32 SCHULTZE, ON THE RETINA. 
more adapted, for the simple perception of light than the 
“cones.” 
We have next to consider the colowr-sense ; that is to say, 
the sense by which qualitative differences in light are per- 
ceived. To judge from our own experience, which in such a 
question can be the only guide, the simplest trials will show 
that, as dusk and darkness approach, the power of perceiving 
colours ceases at a comparatively early stage. In the evening, 
though we may see objects well enough, we are quite uncer- 
tain as to their absolute or relative colour. We may suppose, 
therefore, that an animal which pursues its prey only at night, 
and which habitually frequents dark or obscure places, has 
no sense of colour, or, at any rate, only needs to distinguish 
different degrees of brightness in the different colours, as is the 
case with ourselves in the dusk [or even, in the case of colour- 
blindness, sometimes even in the daytime]. If we assume, as 
from the theory of Young and Helmholtz we are compelled 
to do, that the sense of colour resides in a determinate ana- 
tomical substratum, we are justified in. concluding that that 
particular substratum is wanting in the retina of nocturnal 
animals. The conclusion naturally follows, that the “ cones” 
may, in all probability, be the terminal nerve-organs of the 
colour-sense. 
It should be. borne in mind, however, that the “ cones” 
cannot be regarded as eaclusively confined to the perception 
of colour. The colour-sense necessarily includes the lght- 
sense, or is, as it were, superadded to it; and thus we may 
conclude that, where the colour-percipient cones are sufficiently 
closely aggregated, they may also suffice for the sense of space, 
and thus fulfil all the functions of a retina by themselves 
alone. The only question, therefore, as M. Schultze remarks, 
that can arise, is as to whether it is probable that the ** cones,” 
together with the power of conveying impressions of lumi- 
nosity and space, have not in addition that of conveying im- 
pressions of colour, and whether we have any reason, in like 
manner, to suppose that the “‘ rods’”’ have no such power. 
The author then proceeds to show, in reference to the 
experiments of Purkinje, Hueck, Helmholtz, Aubert, and 
Schelske, that, although the sense of colour exists through- 
out the human retina, it is most acute in proportion to the 
preponderance or number of the “ (1 
€ 
cones” over the “ rods,” 
and that the latter alone are unable to convey impressions of 
colour. He also points out that the probabilities that this 
function resides in the ‘‘ cones” is strengthened by the 
fibrillated structure of the “cones” and their filaments, 
which is in accordance with the well-known theory of colour- 
