The Electrical Response of the Eye to Stimulation by Light 401 



In the case of an eye which has been exposed for a long time to strong 

 light and thereafter maintained in darkn -ss for a few minutes, so that 

 it does not yet differ much from a completely light eye, we see the third 

 substance acting very weakly. 



Fig. 15 may serve as an example of this. The summit C of the third 

 substance is here elevated only 1 mm. or 18 microvolts above its base. It 

 will clearly appear that this amount is both absolutely and relatively 

 very low when the summits B, A^ and C of figs. 5 and 15 are compared 

 one with another. 



Composite Curves. 



Having thus considered the effects of the three substances separately, 

 it is not difficult to analyse the composite curves of figs. 3 and 4 into their 



Fig. 15. — The reaction to light of an eye which has previously been exposed for a long time to 

 strong light and thereafter darkened for some minutes. The third substance is seen acting 

 feebly at C Absc. 1 ram. =0*2 sec. Ordin. 1 mm. =18 microvolts. E, control curve. 

 I, light ; d, dtirkness. 



component parts. The negative deflection A is evoked by the action of 

 the first substance, the summit B by that of the second substance, and 

 the summit C by the action of the third substance. 



In fig. 16 those three reactions are diagrammatically represented as 

 three separate curves. By superposition of these curves we obtain a 

 figure similar to what is shown in figs. 3 and 4. 



In fig. 5, where the lighting duration is 458 sec, there is seen in 

 addition to the deflections of figs. 3 and 4 still another summit A^. This 

 is produced by the darkening reaction of the first substance. As already 

 mentioned, the upward movement of the string which is produced by the 

 darkening reaction of this substance is only of short duration. In agree- 

 ment therewith the summit A^ is superposed in such a way upon the 

 slow wave C that the form of the waves may easily be recognised separately 

 (see diag., fig. 17). 



What has been noted with regard to fig. 5 is also true of fig. 15. The 

 two figures, which differ considerably in outward appearance, nevertheless 



