I 



SELECTIVE SCATTERINf} OP LHillT lOf) 



tioti of ITCN (Bishop), which they attribute to changes in scattering. 

 We can also refer to tlie report of Shil)ata (see page 171). 



Th(^ portion of the nnabsorl)e(I light which does not reach the 

 detector l)ecaiise of scattering, depenrls on the geometry of the 

 apparatus and on (he absorption of light by (he cells. Actually, the 

 contril)ution of scattering to the total attenuation of the; incid(Mit 

 beam often is of (he same order of magnitude as that of absorption. 

 Therefore, some of the reported variations in transmission, which 

 have been interpreted as changes in absorption, could be the result 

 of equally small relative changes in scattering. Experimental evi- 

 dence is needed to eliminate this possibility or to evaluate the con- 

 tributions of absorption and scattering to the observed effect. 



Discussion 



Weigl : Similar, although .somewhat clearer-cut, anomalou.s dispersion curves 

 have been ohsorved in specular reftectioti from solid dyes. 



Rabinowitch : \V hat particularly interested me in this work is that one gets such 

 strong effects from jninor pigments. The example of carotenoids shows that one 

 can detect the presence of some pigm(;nts easier by scattering than by absorp- 

 tion. One sees scattering peaks wheie ones doesn't .see even a shoulder on the ab- 

 sorption curve. Perhaps, when an adecjuate theory is worked out, one will be able to 

 make conclusions as to the state of the different pigments — how densely they are 

 packed, etc. I hope, therefore, that others will try to play with this effect, both 

 theoretically and expeiimentally. 



Another remark that I want to make does go back to the first Gatlinburg con- 

 ference. Three years ago, when Jacobs presented our study of the crystal spectra. 

 Kasha and Commoner attacked his conclu.sions rather sharply, saying that the 

 band shift we had observed may be due entirely to .selective scattering. We were 

 convinced that this was not .so, but could not jjrove it at that time by direct ex- 

 perimental evidence; so the criticism scared us a little and caused us to look more 

 closely into the cjucstion of scattering, first in crystal suspen.sions and subse- 

 quently in live cells. We found that our crystal spectra were not .significantly 

 affected by .scattering, but that selective scattering did in fact occur^both in 

 crystals and in living organisms. 



Latimer's study is thus a consequence of the di.scussions at the preceding Gat- 

 linburg conference. 



Chance: Anomalous dispersion effects, of course, are not unique to Chlorella. 

 An anomalous band at 370 m/z is well known in erythrocytes, and I think it is 

 largely exjilained by a rapid change of the refractive index. 



With regard to Jiatimer's remarks concerning the possible role of .scattering in 

 measurements of .small absorption changes, we have worried about this when 

 measuring intracellular oi)tical density changes. We made light scattering and 

 transmission comparisons, which showed that, in the cytochrome system^ 





