288 RADIATION BIOLOGY 



operations are difficult, and the investigation is being continued with the 

 help of recording instruments.* 



Any method that will give correct and unambiguous analyses for the 

 concentrations of both carbon dioxide and oxygen simultaneously and 

 quickly under a wide variety of light intensities will go a long way toward 

 straightening out some of the differences in manometric results and help- 

 ing to understand the mechanism of photosynthesis. 



Schwartz (1952) tried to repeat with the dropping-mercury electrode 

 the high efficiencies of 3-4 photons per molecule which he had obtained 

 in Burk's laboratory. Using the same methods of algal culture and 

 treatment, he obtained values of 5-8 photons per molecule, with most of 

 the values centering around 8. 



It is extremely significant that the reported high efficiencies of 4 pho- 

 tons per molecule have been obtained only with the manometric method. 

 Some workers urge that the manometric methods, which are subject to 

 these uncertainties, should receive less attention and that greater effort 

 should be devoted to the development and use of methods that give 

 quantitatively and specifically the concentrations of oxygen, carbon diox- 

 ide, and carbohydrate. Other workers, however, contend that, inasmuch 

 as the 4-photon results have all been obtained with manometers, it is 

 necessary to continue the manometric studies in order to show what 

 errors of interpretation may have been made and thus to establish the 

 "about 8" photon value for the manometric methods to bring them into 

 agreement with the nonmanometric values of about 8. 



The type of algae, the conditions of culture, and the absolute measure- 

 ments of energy do not seem to be factors in the disagreement, because 

 they have been so thoroughly checked. An earlier suspicion that the 

 calibrating standard for light measurements might be different has been 

 dispelled. All measurements are now referred back eventually to the 

 U.S. Bureau of Standards standard carbon-filament lamp. Moreover, 

 they have been cross-checked with Warburg's ethyl chlorophyllide 

 actinometer. 



Throughout the whole controversy the constancy of respiration -looms 

 large as an uncertainty. In most of the calculations it is assumed that 

 respiration goes on at the same rate in the light as in the dark. If this is 

 not the case, serious errors can be introduced. The matter is under 

 investigation along several different lines. 



Still more research is necessary to emphasize the nature of erroneous 

 conclusions based on the transient conditions which follow light-dark and 

 dark-light transitions. Transient chemical changes may profoundly 

 affect gas exchange measurements over short time intervals. 



* Added in proof: Yuan (1954, 1955) obtained specific records of carbon dioxide 

 and oxygen simultaneously. Forty measurements of CO 2 averaged 8.7 ± 1.0 photons 

 per molecule while 31 measurements of O2 averaged 9.1 ± 1.2 photons per molecule. 



