DISCUSSION 749 



"i(i, /(.•iliincisicv, 1... r.\l)C)i<-tili<i. 10. I (1954). 



:u. /.erlimcister. I... \c Rosen. A. 1... ,S( inocdcr. W. A.. Tolf^cr. A., and Panling, L., 

 ./. Am. Chiin. Sac. tt."). 1910 ( 191:5). 



DISCUSSION 



Dr. .\rnoli): I would like to i'inc Dr. George Wakl another thorn for 

 his hiurels. It seems to me that the most significant thing about the retina 

 is that it has a hiyered structure, like a chloroplast, and that any theory 

 of vision would have to start with this fact and make real use of it, the 

 same way with photosynthesis. I would suggest that this lecture which we 

 iia\e just heard is very fiine, but it has to do simply with adjusting the 

 sensitivity of the eye to light. A plant doing photosynthesis, when it gets 

 dark, can simply wait until die next morning, but animals have to run 

 around in the evening and sometimes there are cloudy days and they need 

 a terrific adjustment. I think this is just the chemistry of adjusting the 

 amount of pigment to get light sensitivity. I would like to paraphrase 

 Wald's quotation that all biology is chemistry by simply saying that it is 

 not so. The only way tliat chemistry got into biology at all was that when 

 nature went to make organisms, the only materials which occurred in large 

 amounts were atoms and molecules. 



Dr. Wald: Well, I had no time to say, of course, that all chemistry is 

 physics, and I believe that. It is one world, from ultimate particles to the 

 Ninth Symphony. This is what Arnold is talking about. The microstructure 

 of a rod was revealed originally by Sjostrand. The layers which Arnold is 

 talking about are the membranes that compose a pile of flattened sacs, of 

 which there are 500 to several thousands in the outer segment of a rod. The 

 whole thing is derived, as DeRobertis and others have shown, from what 

 was originally intended to be a flagellum or cilium— one of those things that 

 waves back and forth at the end of a cell. Now, these layers appear to be 

 made largely out of the visual pigments themselves. We do not know that 

 for certain, because the great weakness in electron microscopy is that one 

 cannot say w^hat one is really looking at, chemically. The best present sup- 

 position is that the visual pigments constitute in large part those layers, 

 those sacs, those membranes. If not, they would have to come in between, 

 inside the sacs or just outside. Now, what Arnold is inviting us to do is to 

 Ijring these layers into the discussion of vision, perhaps to involve them 

 in a discussion on the level of inductive energy transfer and photoconduction. 

 Is that your thought? 



Dr. Arnold: My thought was that by coming to this lecture, I might learn 

 something about vision that would help us in the photosynthesis problem. 



Dr. Wald: Well, let me say a short piece about that. First of all, I cannot 

 tell you either where this molecule which absorlxd the quantum is in the 

 structure, or how what happens to it results in nerve excitation. But nothing 

 is so naive as— I have the strong temptation to end that sentence— "as a 

 physicist," but I won't. Nothing is ,so naive as the idea that if a quantum 



