Biology Reference
In-Depth Information
(Our experiences of the occurrence and behaviour of rhodopsin are
so highly consistent with M. Schultze's hypothesis about the physio-
logical-chromatic impact of the cones and rods that one just needs to
point to this experience in order to reject the hope that optography
might have something to say about specific colour appeance.)
3.7 Phototransduction of rhodopsin
Kühne also made an important contribution to our understanding
of the transformation process of rhodopsin when activated by light.
Thus, like Boll (
1877
), he found that rhodopsin first decomposed to
a photoproduct that he called visual yellow (Sehgelb), and that this
photoproduct further decomposed to yet another photoproduct, visual
white (Sehweiss). Based on this finding, he made the important distinc-
tion between the photopigment (Sehstoff) and the photoproducts of the
pigment (Sehreger) and suggested that it was the photoproducts that
generated the neural activity in the retina (Kühne,
1879
, p. 327).
Moreover, he discovered that rhodopsin may regenerate in
two quite different ways: by a process which he named 'Anagenese'
where the photoproducts visual white and visual yellow in the outer
segment of the rods returned to rhodopsin and by another process
which he called 'Neogenese' where rhodopsin, after having been
completely bleached, was rebuilt by new substances (Kühne,
1879
,
pp. 317-323). The 'Anagenese' was assumed to proceed much more
quickly than the 'Neogenese'. Hence, the speed of the dark adaptation
process would be determined by the relative contribution of these two
processes - complete bleaching would give the slowest recovery.
3.8 P a r i n au d a n d K ö n i g : e a r ly
reformulations of the duplicity theory
Soon after the discoveries of Boll and Kühne, compelling new
evidence in support of rhodopsin as the photochemical substance
responsible for night vision was provided by Parinaud (
1881
,
1884b
,
1885
) and König (
1894
). On the basis of their discoveries they both
presented their own version of the duplicity theory and have later
