Biology Reference
In-Depth Information
his far-reaching speculations have proved successful in promoting
the development of the duplicity theory. Indeed, his theory may be
seen as a test of the fruitfulness of providing comprehensive and
speculative theories within vision research. In the following sections
we present his theory in some detail.
5.2.1 G. E. Müller's speculation on the phototrans-
duction in rods
In agreement with Kühne (
1877a
), Parinaud (
1881
,
1885
), König (
1894
)
and von Kries (
1894
,
1929
), G. E. Müller held that rhodopsin was the
photopigment of twilight vision and, consequently, that its spectral
decomposition determined spectral sensitivity in a dark-adapted state
at low test intensities (G. E. Müller,
1897
,
1923
). Also, he assumed
that there was a continuous approach toward a state of equilibrium
between decomposition and regeneration of the photopigment when
it was acted upon by light.
At variance with Kühne, Parinaud, König and von Kries, however,
he presumed that rhodopsin was but an optical sensitizer (optischen
Sensibilisator). Its decomposition by light sensitized and, hence,
increased the turnover of a base substance A ('Ausgangsmaterial') to
a substance W ('W-material'). As the amount of this second substance
increased, it was transformed into a third substance, substance V
('V-material'). The latter process, then (the change from the W to the
V substance in the outer segment of the rods), was thought to be
responsible for the 'white-' related neural activity ('W-Erregung') of
the rods (G. E. Müller,
1923
). An important and original consequence
of this line of thinking was that rod sensitivity did not solely depend
on the amount of rhodopsin, but also on the amount of the substance
A available in the outer segment of the rod receptors.
5.2.2 Cones may inhibit regeneration of rhodopsin
In order to obtain a better understanding of how rod activity may
change with light level, G. E. Müller (
1923
) made an extensive review
of the available evidence concerning so-called rod monochromats.
