172 L. N. M. DUYSENS 



within a time of that order. In general the changes take place in a time of one or 

 several seconds. [Except for Witt's effects. — Ed.] 



Frank Allen : I would not expect the temperature effect to be so selective over 

 the si)ectrum. 



Rabinowitch : Dr. Shibata, I wonder whether your effects are not the result of 

 scattering. Your changes might result from so-called anomalous dispersion, which 

 is associated with changes m refractive index in the vicinity of an absorption peak. 

 When you change the temperature, even slightly, you do change the index of 

 refraction of the colored particles, in this case, of the grana. 



Frenkel : I feel that the 40° C. temperature maintained by Dr. Shibata in his 

 work is rather unphysiological. I would be quite cautious in interpreting the 

 effects. Though some cultures have been acclimatized to 40° C, normal cultures 

 can only stand about 30° C. 



Shibata : I believe the Rhodospirillum were unharmed by the temperature. 



Duysens : I think we have evidence which shows that the decrease in absorption 

 at 880 m/x in Rhodospirillum is not a temperature effect under the conditions of the 

 experiment. 



If the change in transmission caused by illumination is measured first with the 

 bacteria in distilled water and then in a culture medium, we get strikingly different 

 results. In the first case there is a very great change m transmission; in the second 

 a slight one. If the change were due to a temperature effect, you would not expect 

 this difference because the temperature effect should be about the same for the 

 two cultures. 



Myers: Is that a reversible effect? 



Duysens : Completely reversible. 



Chance : Did it occur to you that the metabolism would increase at the higher 

 temperature and might therefore give rise to the absorption band that j^ou 

 observe between 400 and 450? 



Also, some physical properties of the bacteria might change with the rate of 

 metabolism. 



Do you think that j'ou are recording the intensification of an absorption band 

 already pre.sent or the shift of a band position with temperature? 



Wassink : Is there any harm in assuming that, since these obviously are conse- 

 quences of the related metabolism, they may be brought about as well by 

 light as by temperature? I mean by a different pathway probably, but just by 

 attacking the same compounds, let's say cytochrome or whatever they are, that 

 are involved in these oxidation-reduction changes. 



French : I think everybody would agree that that happens. 



Chance : I would like to concur in a suggestion made by Dr. Duysens. We rou- 

 tinely use a gray filter of a density of 4 or 5 between a half-voltage tungsten lamp 

 and cell in order to cause a measurable effect. This light intensity might be of the 

 same order of magnitude as the light which you get from the Gary spectropho- 

 tometer, and perhaps sufficient to cause a light effect. If the hotter cells have a 

 sensitivity to light different from that of the colder cells, you might well get just 

 the effects you record: an effect of temperature upon the photochemical reaction 

 and not upon the absorption spectrum per se. 



Rabinowitch: Let's say, in this light, the clilorophyll molecule absorbs a 



