172 
Ist equal limit values can be obtained both when the after-images 
are still extant and when they have afterwards disappeared. 2'y Two 
succeeding limit values can also indicate a regular increase of the 
prestation, when the same subjective intensity of the after-images 
is stated. 3'y The weakening or strengthening of the subjective in- 
tensity of the visible after-images (reached by means of an adequate 
modification of the illumination of the sereen round the flickering 
hole) remains without influence on the shape of the curve. 
From the comprehensive problem of the nature of visual fatigue 
it appeared to me, that, for a concrete experimental answer, in the 
first place the question must be solved: where is the place of the 
processes of fatigue? Is it peripheral, central or both? In order to 
approximate the answer | have applied the following method. Two 
progress curves obtained by monoculary determinations at the same 
eye are compared together. In one series the same eye is 
fatigued, on which the determinations of the limit value are executed 
(direct penetration), in the other series on the contrary the stimulus 
of fatigue on the other eye (consensual penetration). 
The experiments applied under constant adaptation of the not 
fatigued eye showed the image represented in table Il (p. 173). 
The results can be summarised in the following rules: 
1. There exists a consensual fatigue of the eye. 
2. The first occurring decrease of the prestation is greater at the 
direct fatigue than at the consensual one. In the examined limits 
of the intensities of the light this relation depends neither on the 
brightness of the flickering bole nor on the duration of the fatigue. 
3. At the direct fatigue the norm is generally reached a little 
later than at the consensual penetration. 
4. Up to the norm the curves have a tolerably equal process. 
5. Then however the essential difference appears, that the direct 
fatigue causes the well-known over-compensation, whicli did not 
occur with the consensual irritation in the examined limits. 
Points 2 and 3 may be summarised in the thesis, that the direct 
irritation of the eye causes greater fatigue than the consensual one. 
The explanation of this fact might be found in the self-evident cir- 
cumstance, that in the case of the consensual penetration there is 
only a central component of the fatigue extant, whilst at the direct 
irritation there is still the dissolution (kataboly) of the substances, 
that are lying in the irritated eye itself, i.e. peripherally. 
With this hypothesis of two components of the visual fatigue 
point 5 can be interpreted as follows. The results of the overcom- 
pensation are in the first place characteristic of the restitution of 
