DISCUSS/ ON 815 



whole log sensitivity curve up or down l)y a certain amount. And the eflFect 

 upon the other will be to shift its curve by a different amount. So the efTect 

 upon the curve of the weighted mean (which is tfie ganglion sensitivity) 

 will lie a xicrlical shift f)y an amount which is the weighted mean of the two 

 receptor shifts. It is clear that this purely vertical shift will be appreciated 

 as "no change in spectral sensitivity with adaptation to colored lights." And 

 this is what Donner and I found happened with the rod-plus-cone input of 

 our ganglion cells. Ihis is why I feel that a spectral sensitivity which does 

 not change in chromatic adaptation cannot exclude the possibility that it is 

 compounded of mixed pigments and mixed receptors. 



Dr. MacNichol: We are very tentative about describing these pigments 

 and I made my apologies. We did it saying that this is the best we can do 

 at the present time. Now I am not quite clear. If you change the relative 

 proportions of these two pigments and then sum up the logarithms, you get 

 a cur\e which does not shift its maximum over? 



Dr. Rushton: If the curves just go up and down you won't. If you alter 

 the proportions at which you are going to add them, it will. But dark 

 adaptations only send them up and down and do not alter the proportions. 



Dr. Wolbarsht: Yes, but suppose one is sitting still, and the other is 

 moving. What do you do with it then? In our data, we have two threshold 

 curves from the same cell. Their peaks are widely separated. The relative 

 sensitivity of one curve changes while the relative sensitivity of the other 

 curve is standing still, yet the shape of the curve that is moving stays 

 constant. That seems to indicate that there is no interaction. 



Dr. Rushton: No. 



Dr. Wolbarsht: Well, that's what we have. 



Dr. Rushton: You don't prove it really. 



Dr. MacNichol: I can't argue with you until I have worked this thing 

 through. I guess we will have to work it through. 



Dr. Thimann: When the light is off in the on-off experiments, is it absolute 

 darkness? 



Dr. ISIacNichol: It is absolute darkness. Well, it's absolute darkness as 

 good as our shutter is. That is 7 log units. 



Dr. Kasha: I'd like to ask if there are any electron microscope studies on 

 the eye retinal structure showing some kind of trend with evolutionary com- 

 plexity of the animal. 



Dr. Hartline: Yes, there are numerous ones. The arthropods show the same 

 general structure that Grossman has shown for the insects, the microvilli of 

 the retinular cell surface. The scallops have laminations not unlike the 

 vertebrate rods, again derived from cilia. There have been numerous such 

 studies. 



Dr. Linschitz: I'd like to come back to the question of energy migration 

 in the rods. Sjostrand's electron microscope data show that the rod micro- 

 structure consists of a pile of laminations, each of which has a typical sand- 



