Biology Reference
In-Depth Information
2.
Anatomical interpretation of the theory. Cones and Rods. Uniqueness
of the fovea. Rhodopsin
.
Under this second heading, von Kries referred to a number of
experiments which demonstrated the complete absence of the
Purkinje shift in the rod-free foveal region. The evidence he
found supported the suggestion that the cone receptors were
the anatomical substrate of day vision, while the rods were the
anatomical substrate of twilight vision. An even stronger argument
in favour of this suggestion was the close relationship found
between the spectral sensitivity of twilight vision and the degree
of decomposition of rhodopsin with wavelength. Surprisingly, von
Kries did not refer to König (
1894
), but to Trendelenburg, who
much later obtained results similar to those of König (see von
Kries,
1929
, p. 691).
Lastly, the corresponding time between regeneration of
rhodopsin and the sensitivity increase during dark adaptation
measured extrafoveally (both processes take about 30 min to approach
the final level) were mentioned as important evidence supporting the
duplicity theory.
3.
Isolation of twilight vision. Congenital, total colour-blindness.
Nyctalopia. On comparative anatomy.
Here, under this third heading, von Kries presented experiments which
showed that the spectral luminosity function in twilight vision was
approximately the same and remained essentially invariant within
the scotopic intensity range when measured in trichromats, dichro-
mats and rod monochromats. In
Fig. 3.1
the spectral sensitivity of
rods and cones obtained at 30° extrafoveally are shown. As can be
seen, the sensitivity difference between rods and cones is large in the
short-wave and small in the long-wave region.
Finally, Schultze's observation that the relative number of rods
to cones differed in the retina of diurnal and nocturnal animals, and
the investigation of 'l'héméralopie' by Parinaud (
1881
), were found to
support the duplicity theory.
