1112 



THE LIGHT FACTOR. II. QUANTUM YIELD 



CHAP. 29 



6. While Emerson and co-workers were able to closely reproduce the 

 measurements of Warburg and Burk (I/7 — 3-4), the results became quite 

 different if light and dark periods were lengthened to 30 minutes or if 

 the vessel shape h2 (fig. 29. 4A) was substituted for hi in the two-vessel 

 combination. Either change led to 7""^ > 9, with the same cells which 

 gave values of 3-4 by following Warburg and Burk's specifications. These 

 changes should diminish errors due to different physical lag, though per- 

 haps not eliminate them, nor overcome all the disadvantages in the tech- 

 nique of Warburg and Burk. However, it is significant that the yield was 

 found to be dependent on both timing and vessel shape. 



h, H Hj 



Fig. 29. 4A. Manometric vessels for two-vessel method of quantum yield 

 measurements. H, vessel with small gas space; hi hi, vessels with large 

 gas volume. 



7. Warburg and Burk have calculated — AO2/ACO2 values of the 

 order of 1(±0.2) for the ''light effect" in the two-vessel experiments. 

 However, this does not prove that no significant carbon dioxide burst and 

 gulp had occurred in their experiments, but — as already was explained on 

 page 1101 — merely that the "gulp" in the dark period compensated more 

 or less completely for the burst in the light period. This compensation is 

 inevitable in a series of light-dark cycles in which approximately stationary 

 conditions are established after a few cycles. Separate calculation of 

 — AO2/ACO2 in light and in darkness (suggested on p. 1102) gives — ^in the 

 few cases where the necessary data are provided by Warburg and Burk — 

 values quite different from 1, with deviations in the direction required by 

 the burst-and-gulp hj^pothesis. 



8. Warburg and Burk's experiments Avith white (or red) background 

 light have additional uncertainty because they were carried out by consecu- 

 tive, and not alternate, measurements in the two vessels. Earlier experi- 

 ments of Emerson and Lewis had indicated that the burst occurs not only 

 upon change from light to dark, but also upon change from one light in- 

 tensity to a higher one; thus, the interpretation of experiments with light- 

 compensated (or overcompensated respiration as "base line" can be the 

 same as suggested above for the light-dark experiments. 



9. To sum up the conclusions of Emerson and co-workers, the experi- 



