28 
ness (see fig. 4), a good image may be got of the geometrical 
increase of the sensitiveness during the adaptation. In this figure 
the logarithm of the value of sensitiveness has also been represented, 
which is finally reached after complete dark-adaptation after 13 — 2 
hours. When however as ordinates the sensitiveness itself is repre- 
sented, the ascent of the curve shows the rate of the arithmetical 
increase of the sensitiveness as Piper (1903) carries it out and dis- 
cusses it for the adaptation of the sense of sight. 
When therefore we would graphically represent the adaptation 
of these cells in the way of Preer, it would give the impression 
(see Table IV), that there is but a very slight adaptation in the 
first 30 min. that after 70 min. only '/, of the dark-adaptation is 
finished, and only after that the adaptation progresses fastest (curve 
steepest). If Piper’s adaptation-curves are converted, by representing 
the values of sensitiveness instead of the sensitivenesses themselves, 
and if they are compared with the same representation for the cell, 
the strongest rise 6f sensitiveness in man is found earlier than in 
Piper’s report and only then it becomes quite clear that the adap- 
tation-process of our sight-impression is mathematically not so simple 
as with these cells. For three curves with an average course (II, 
III and IV of Prirer’s observers) the logarithm of the values of 
sensitiveness has been represented in fig. 4. In the main 4 phases 
may be distinguished: a rather rapid one (first 3—6 min.), a very 
rapid one (3—6 to 8—12 min.) a rather rapid one (8—12 to 20—-27 
min.) and a very slow one (after 20—27 min.). When comparing 
we get the impression, that with the cell-adaptation we have to 
deal with a simpler process, though the same phases may be faintly 
distinguishable. 
We have still to add that we determined the thresholds in these 
cells with fixed quantities of light, while for the human eye only 
intensity-thresholds have been determined. That makes the comparison 
more difficult. Determination of quantity-thresholds for the eye might 
picture the adaptation-process differently and more accurately. More- 
over Piper is wrong in not giving the exact intensity to which the 
eye was previously exposed, in beginning his first observations only 
after about 1 min. dark without an observation z light and in 
taking this first observation as zero in his curves. 
Finally we may observe, that the width of adaptation with these 
cells is 1:350.000. With man it is according to Piper only 1: 2 
to 8000; in consequence of the measuring of the intensity-threshold, 
and the mis-stated initial intensity a perfect comparison is not possible, 
