DISCUSSION 473 



first one for the reason you mentioned. In the chemical picture the mctastable 

 state is sujiposed to produce a chenncally changed substance (the enol 

 complex, see, c.i>., the discussion after Clalvin's paper) , and it (an li\e for 

 a number of seconds i)efore it \anislies by back reactions. 



Dr. Platt: I would like to make an extension of some of the thoughts we 

 have all had. When we get physical chemists together with biologists, we 

 should not talk entirely al)out theory or interpretation. We should also 

 talk tools, because it is entirely possible that physicists and physical chemists 

 mav be al)le to suggest certain tooling effects which might be useful to 

 biologists and vice versa. It is possible that biologists may be able to suggest 

 certain types of measurements they woidd like to make which they cannot 

 make with existing tools. At the Brookhaven Conference last October we 

 had almost a half day on the discussion of possible tools. I would like to 

 mention two possible tools which it seems to me would be of great advantage 

 in distinguishing one pigment from another in a cell, or one complex from 

 another in a cell without taking the cell apart. Now, this means that we 

 have to find a physical method which we can apply externally to the cell 

 with minimal damage. The ones that I would like to mention that we can 

 put into the cell from outside without wrecking it perhaps are light, changes 

 of temperature, and changes in pressure. In the case of light, of course, we 

 have been discussing some of the changes that are observed in the form of 

 bleaching. Let me mention one thing that has not been mentioned and 

 which might be illuminating— and I don't mean that as a pun— for some 

 of these studies, that is, to try polarized light in the photo-bleaching experi- 

 ments. The reason is that the bleaching should be polarized if the incoming 

 light is polarized, if the bleaching is in the same molecule that is absorbing 

 the light. So one would be able to correlate one peak with another peak 

 in the same spectrum by finding a concomitant polarization and say that 

 these are probably the same molecule or closely associated molecules. Peaks 

 which don't have polarized bleaching, then, might be further away or more 

 randomly arranged. This might be an additional cheap piece of information. 

 In the case of temperature we have seen a number of high temperature and 

 low temperature spectra. Let me emphasize one feature when we go from 

 a high temperature spectrum to a low temperature spectrum. If we have 

 several vibrational peaks in the same molecule which we will call 0-0, 0-1, 0-2 

 one would not expect to change much the spacing between these peaks for a 

 given molecide with temperature. However, if we have two different elec- 

 tronic transitions which lie in the same region and which have a different 

 electronic structure, or come from a different molecule, they will shift by 

 different amoimts with temperature. So there will be relative shifts of one 

 set of peaks with respect to the other, which proves that the set which shifts 

 together is one electronic transition, or one pigment, or one molecule, or 

 one complex and the other set which has a different amount of shift lielongs 

 to another, very probably. The same argument may be made for pressure, 



