OXYGEN EXCHANGE DURING THE SHORT INDUCTION PERIOD 



1327 



In contrast to the qualitative observations of Blinks and Skow, the re- 

 cordings of Damaschke et at. were used to evaluate the absolute yield of 

 oxygen production during the burst, and its net yield in a complete light- 

 dark cycle; these calculations will be dealt with in more detail in chapter 

 37D. Depending on (unspecified) conditions, the duration of the "gulp" 

 was found in these experiments to vary from a few seconds (as in fig. 33. 6B), 

 to one, or even ten minutes. (Among widely varied conditions, one notes 



30 seconds 



Fig. 33.6B. Polarographic recordings of Oo liberation by Chlorella (160 mm.' 

 cells per 80 cc.) exposed for 3, 8 and 28 sec. of additional illumination, on top of 

 continuous light sufficient to compensate respiration (after Damaschke, Todt, 

 Burk and Warburg 1953). Time scale from right to left; gulps of O2 are seen to 

 follow the exposures. 20% CO2, 20° C, X = 644 m^. 



the carbon dioxide concentration, which was 5%, 20% and even 54% in 

 the several experiments illustrated in the paper.) 



The wide variation in duration (and volume) of the oxygen bursts and 

 gulps observed by Warburg and co-workers in manometric, as well as elec- 

 trochemical measurements in differently pretreated ChhreUa cultures, 

 makes their interpretation as revelations of an intrinsic thermal component 

 of the reaction sequence of photosynthesis rather implausible. This view 

 is supported by evidence from other investigations described in this chapter, 

 such as the polarographic studies of Brackett, in which no oxygen burst 

 was noted at all (while the gulp was clearly noticeable, but much less 

 prominent than in Warburg's curves) ; and Brown's mass-spectrographic 

 data (in which the respiratory oxygen consumption of Chlorella was 



