284 RADIATION BIOLOGY 



the time lag in the manometers and in the biological reactions lead to a 

 very complicated situation that can give different rates of change in the 

 gas pressure depending on the conditions prevailing in the manometers 

 and on the pretreatment of the algae. Starting in 1939 with the investi- 

 gation of Emerson and Lewis and continuing to the present time, Emerson 

 and his associates have obtained consistently a quantum requirement of 

 8-10 photons per molecule, and they conclude that in Warburg and 

 Burk's experiments, which indicated a requirement of about 4 photons 

 per molecule, insufficient allowance was made for the time lag, and the 

 differential time lag in particular. These time lags may make large 

 errors in the two-vessel manometric method. The manometric measure- 

 ments of Emerson and Lewis gave results of exceptionally high precision. 



There is no controversy among those who determine the energy effi- 

 ciency by nonmanometric methods. These methods always lead to 

 quantum-requirement <i>~^ values of about 8 photons per molecule, with 

 occasional values somewhat less. With the exception of the work of 

 Warburg and Burk and their associates, most of the other workers using 

 the manometric method have obtained values in agreement with those 

 obtained by the nonmanometric methods. 



Petering cf al. (1939) used a polarigraphic method specific for oxygen 

 and obtained values of about 10 photons per molecule. Stauffer (1939) 

 used a two-vessel manometric method at the same time with the same 

 algae, the same cultural techniques, and the same light standardization. 

 He too obtained independent values of about 10 photons per molecule. 

 Rabinowitch (1951) concludes that "the quantum requirement of 10 ± 2 

 represents the true measure of the efficiency of the common primary 

 photochemical process. The quantum requirements of much less than 

 8 reported by Warburg and Burk in acid media are the only ones which 

 do not fit into this picture. Whether this discrepancy is caused by a 

 systematic experimental error, as suggested by Emerson and coworkers, 

 or to the substitution for true photosynthesis of a partial reversal of 

 respiration requiring a smaller number of quanta is an independent and 

 controversial question." 



After further perfecting of the polarigraphic method for oxygen, Moore 

 and Duggar (1949) obtained very consistent results, as shown in Fig. 4-1. 

 It is to be noted that in this method, which measures only the dissolved 

 oxygen (without the complication of carbon dioxide and the transfer of 

 gases into the gas phase), quantum requirements of 9-11 photons per 

 molecule were obtained under conditions where respiration exceeded 

 photosynthesis and where photosynthesis exceeded respiration. Further- 

 more the same value was obtained when changing from dark to light or 

 when changing from a given hght intensity to a higher light intensity. 

 Within the limits of accuracy of the experiments, the results were the 

 same for red, blue, or green light. 



