Biology Reference
In-Depth Information
conditions, the rod receptor system was not equally activated in the
test and comparison fields.
König's third thesis is the most original one. It suggests, in
opposition to both Schultze (
1866
) and Parinaud (
1881
,
1885
), that rods
may play an important role in colour vision. Previously, Ebbinghaus
(
1893
) had speculated that the photopigments of rods could be identi-
fied as the yellow-blue substrate postulated by Hering (
1878
). Thus,
the action of light on rhodopsin and visual yellow (a photoproduct
of rhodopsin) was supposed to give rise to the sensation of yellow
and blue, respectively. In agreement with Ebbinghaus, König (
1894
)
assumed that the formation of visual yellow was necessary in order
to obtain the primary blue sensation. Consequently, he held that the
rod-free fovea was blue-blind. In opposition to Ebbinghaus, however,
he suggested that activation of rhodopsin generated achromatic
instead of yellow sensations - a suggestion based on his finding that
light appeared achromatic, not yellow, under scotopic conditions
where rhodopsin was responsible for vision.
In order to reconcile his assumption that visual yellow and
rhodopsin situated in the same receptor generated two qualitatively
different sensations with the specific fibre-energy doctrine, König
(
1894
, p. 591) referred to complex processes originating in the
sensorium. Other ways to explain this would have been to accept the
ad hoc assumption of Helmholtz (
1867
) that different qualities may
be transmitted through the same fibre or, alternatively, to presume
that two different fibres, one subserving achromatic sensation, the
other blue, were connected to each rod.
3.12 The duplicity theory of von Kries
In contrast to Schultze, Boll, Kühne, Parinaud and König, von Kries
(
1894
,
1896
,
1911
,
1929
) did not provide compelling
new
evidence in
support of the duplicity theory. Instead, he fulfilled the important role
of promoting its general acceptance by presenting a comprehensive
discussion of all available evidence in favour of the theory, including
his own accurate experimental results (see von Kries,
1929
).
