750 LIGHT AND LIFE 



is received by a rhodopsin molecule somewhere high up in a rod outer 

 segment, and if only you have some way of transferring the excitation down 

 to the base, you would have solved the problem of nervous excitation. The 

 trouble is that I do not know any better what to do with a molecular excita- 

 tion at one end of a rod than at the other. To move that excitation around, 

 when I do not know what to do with it, is sheer nonsense. I just do not yet 

 know what wants to be done with the excited molecule, and that is that. 



Dr. William Hagins came to the Faraday Society meeting on Biological 

 Energy Transfer a year ago, and described a series of ingenious experiments 

 in which he attempted to demonstrate inductive resonance transfer of excita- 

 tion in rods. So far they have not worked. We have another experiment in 

 mind. Hagins has told me it is not going to work. Maybe he is right. 



Let me say a last thing. For heaven's sake, don't confuse vision with photo- 

 synthesis. The way to learn from comparing those two processes is not by 

 saying how much are they alike, but how and why they are different. The 

 job of photosynthesis is to use the absorbed energy of light to do chemical 

 work. The more efficient it is in turning light into work, the better it is 

 working. On the contrary, the light absorbed in vision is not used primarily 

 to do work, but to pull a trigger. What is needed is not work, but molecular 

 excitation. There is no evidence whatsoever that light contributes energy 

 to the net process. 



Dr. Hartlink: The sad fact is that we just do not know what the primary 

 photoreceptors do. We do not understand the excitation process. Nobody 

 has seen for sure the immediate result of excitation of a primary visual 

 sensory receptor, except perhaps in one case, and that is the eye of a scallop. 

 Pecten. Limulus is more complicated, so we can only speculate about it. 

 Until we get information about the actual responses of the primary receptor 

 cells, we should remember that speculation is useful but it doesn't get us 

 very far. 



Dr. Rabinowitcii: I think, George, you are not being fair. VV^e really 

 want to find out what the difference is. You see, as long as we only knew 

 that membranous structures existed in chloroplasts we thought that they 

 are there to permit energy migration, and utilization of diffusely absorbed 

 energy in one spot. When we now see that this structure also occurs in 

 the visual rods, we can interpret this in two ways: (1) with Arnold we can 

 suggest that there must be energy migration also in the rods; or (2) we can 

 say, maybe we were altogether wrong, and layered structures in chloroplasts 

 have no relation to energy migration. Maybe, such structures can do some- 

 thing (juite different from energy migration. That is what we would like to 

 understand. My feeling is that, when you have this kind of structure— 

 large-surface two-dimensional elements, you can achieve two things. You can 

 improve energy migration, and you can improve chemical diffusion, because 

 you provide a big surface, like a frying pan, where chemical reactions can 

 occur in good contact with whatever is on the outside. Which one is im- 

 portant for photosynthesis and which one in vision, we do not know. In 



