362 HENRY LAURENS AND HENRY D. HOOKER, JR. 



only distantly, if at all, related, the wave-lengths of maximal 

 stimulating efficiency are practically the same? This does not 

 mean that we cannot compare the effects of lights of different 

 wave-lengths on photosensitive protoplasm with the effects on 

 the photosensitive substance in the eye of man, as indicated by 

 their respective relative stimulating values. 



In this connection attention is called to the objections stated 

 by Loeb and Wasteneys ('16, p. 224; Loeb, '18, p. 102) against 

 the drawing of conclusions from comparisons made between the 

 sensations of brightness in color-blind human beings and the 

 wave-lengths of maximal stimulating efficiency for lower organ- 

 isms to the effect that these lower organisms are therefore also 

 'color-blind.' The two photosensitive substances, visual purple 

 and the photosensitive substance in the organism in question, 

 are merely affected in a similar way by the same wave-lengths. 



We do not wish to seem hypercritical, but feel that attention 

 should also be called to the probability that the determinations 

 of the wave-lengths of maximal efficiency in bleaching visual 

 purple, and of those maximally absorbed by it, will be found to 

 be erroneous. The work of Trendelenburg ('04) is far from per- 

 fect, particularly in the application of the energy corrections and 

 in the determination of the region of maximum absorption 

 (Garten, '06, '08), as indicated by the shifting of the relative 

 absorption values. Furthermore, Henri ('11) has ascertained 

 the threshold energy, the bleaching effect on visual purple, and 

 the amount of light absorbed by it at various wave-lengths with 

 due consideration to the distribution of energy in the spectrum. 

 These three factors all follow the same course with maxima be- 

 tween X520mAt and X500m/x. Also Bender ('14, '16) has recently 

 found that the luminosity curve for the totally color-blind eye 

 and for the peripheral field of the normal, dark-adapted eye 

 has a maximum between X515m/i and X520m//. 



Perhaps importance may be attached to the fact that the 

 chemical processes in the retina are assumed to be pseudorevers- 

 ible reactions, while there is as yet no positive evidence that any 

 other reactions involving photosensitive protoplasm are of this 

 type. Furthermore, visual purple is an optical sensitizer, al- 



