W. A. H. RUSHTON 721 



REFERENCES 



1. Dartnall. H. ). A., (iooclcvc, C. F., and I.ytligoc, R. |.. I'roc. Roy. Soc. I.oiuloii 



A. IW. L'Ki' (1<W). 

 '_'. DoiiiKM. K. ()., aiui Riislitoii, W . A. II., /. riixsial., 149, :{I8, yZ7 (l'J;VJ). 

 :?. Fuortes, M. G. F., J. Physiol., 148, 14 (1!)")9). 



4. Hccht. S., Shlaci. S.. and IMicniie, M. H.. /. C.eu. Physiol.. 25, 819 (1942). 

 ."). Kocuig. .\.. S. H. Akdd. Wisscuscli. Berlin, bTi (1894). 

 (i. Riggs, L. A., and Graham, C. H.. ./. Cellular Comp. Physiol.. 2(). I (191,")). 



7. Riishton, W. A. H., ]. Physiol., 134, 11 (19,%). 



8. Rushton, W. A. H., Ann.N. Y. Acad. Sci., 74, 291 (1958). 



9. Stiles, W. S., Documenta Ophthalmol, 3, 138 (1949). 



10. Stiles. \\\ S., Proc. Nat. Acad. Sci. U. S., 45. 100 (19,')9). 



11. Trendelenburg, W., Z. Psychol. Physiol. Siunesorg., 37, 1 (1904). 



12. van der Velden, H. A.. Physica, II, 179 (1944). 

 i;^. Wald. G., .Science. 119. 887 (19,")4). 



14. Wald, G., Brown, P., and Smith, P., J. Gen. Physiol., 38, 623 (1955). 



15. Yeandle, S., Am. J. Ophthalmol., 46, (No. 3, part 2), 82, (1958). 



DISCUSSION 



Dr. Wald: I have a short and trivial question. What is A' in that hist 

 shde that you showed us? 



Dr. Rushton: What you mean is how many molecules are there in the 

 compartment? 



Dr. Wald: No, I want to know what exponent goes on intensity. 



Dr. Rushton: The experimental relation is log Id = Ax, where A is about 

 40 for rods, 4 for cones. 



Dr. Wald: That's the other way to look at it. 1 hat's all right. 



Dr. Franck: I missed that point. Is the threshold you spoke of that of 

 the rods or that of the cones? 



Dr. Rushton: I was sometimes dealing with cones and sometimes with 

 rods. To which experiment were you referring? 



Dr. Franck: I want to know whether you can bleach \ery much of the dye 

 present in the rods. 



Dr. Rushton: Yes, we can bleach all the dye present in the rods and all 

 the dye present in the cones. The curve starts from zero, because that was 

 complete bleaching. However, if you press me why I know it is completely 

 Ijleached, I can only say becau.se I cannot bleach any more. That is not a 

 very good answer, of course. If we leave the light on, we can apparently 

 bleach everything in half a minute in bright light, for if we leave the lights 

 on for a further 5 minutes, there is no substantial change. In half a minute 

 we can bleach all that is l)leachable. 



Dr. Franck: .All that can be bleached, but what percent is that of all the 

 dye that is present? In the cones you proljably bleach everything. But is 

 the structure in the rod such that you can bleach everything? That is my 

 question. 



