QUANTUM YIELD MEASUREMENTS BY THE MANOMETRIC METHOD 1103 



that the voUime of the carbon dioxide burst depends on all these conditions ; 

 the .statement that the Qp measurements were made "under the conditions 

 of quantum yield determinations" was therefore not justified. 



Rabino witch (1947) pointed out that experiments show the integrated 

 volume of the "burst" to change only little with light intensity, the main 

 effect of the latter being on the suddenness of the burst. This relation is 

 to be expected for photochemical emptying, with a high quantum yield 

 (perhaps as high as 7 = 1) of a "carbon dioxide reservoir," containing a 

 finite volume of carbon dioxide (the exact volume being dependent on con- 

 ditions that prevailed prior to illumination) . If the volume of the reservoir 

 corresponds to about one molecule carbon dioxide per molecule chlorophyll, 

 the time required for complete emptying must be of the order of the time 

 required for each chlorophyll molecule in the suspension to absorb a quan- 

 tum of light; in the dense suspensions and in the low light used for the 

 quantum yield determinations, this time is of the order of ten minutes (c/. 

 chap. 32) ; this is then the expected duration of the burst. In stronger 

 light, the burst will be proportionally shorter. 



If the volume of the burst increases only little or not at all with light 

 intensity, its importance at 3780 erg/cm.^ sec. would be much smaller 

 than at 320 erg. /cm. ^ sec. (where the value 7 = 0.25 was found). 



Emerson and Nishimura (1949) criticized also other experimental 

 aspects of Warburg's work. They pointed out that the use of equal liquid 

 volumes and different gas volumes in the two-vessel method (Emerson and 

 Lewis, cf. fig. 25. 3B) assured better comparability of the gas exchange than 

 Warburg's use of a single vessel filled with different amounts of liquid (since 

 the efficiency of gas exchange between the two phases depends on the 

 volume of the liquid). Objection was raised also to Warburg's time 

 schedule, which involved consecutive runs first with the more concentrated 

 and then with the more dilute suspension. Because of continuous change 

 in the rate of respiration of cell suspensions, only simultaneous exposure 

 and darkening of tAvo aliquots of the same cell material could vouchsafe the 

 required high degree of their physiological comparability. Emerson and 

 Lewis themselves did not quite meet this requirement: they, too, worked 

 first with one, and then with the other vessel, but in contrast to Warbvu'g, 

 they used a fresh aliquot of the stock suspension for each experiment (con- 

 sidering this a less objectionable compromise than the use of a single sample) 

 first for a series of measurements in a smaller volume of liquid and, after 

 dilution, for a second series of measurements in a larger volume. 



The discussion of these apparently minor details points to the great 

 practical difficulty of the (theoretically so simple) two-vessel method: it 

 rests on the assumption that the obsei-ved difference between the two 



