230 L. HORWITZ AND F. L. ALLEN 



0.8 cell volume per hour), although large amounts of oxygen are being 

 consumed (in the oxyhydrogen reaction). 



TABLE I. Mass Spectrometer Data on the Gas Exchange of Adapted Scenedes- 



mus (Temperature is 20.6°C.) 



A ratio indicative of the relative amounts of true photoreduction 

 and photosynthesis which the algae are carrying on is that of carbon 

 dioxide consumed photochemically to oxygen produced in the light. 

 If there is only photosynthesis, this figure is close to 1 and if there is 

 only true photoreduction, it is infinity. Combinations of the two 

 processes will give intermediate values. The ratio has been calculated 

 by assuming that the carbon dioxide fixation concomitant with the 

 oxyhydrogen reaction occurs in the light as well as in the dark. The 

 results are tabulated in column 4 of Table I. 



In some of the experiments an ultraviolet treatment had just pre- 

 \-iously been administered to the algae. However, there is no reason 

 to believe that this should invalidate the results. The data on carbon 

 dioxide production indicate the cells were adapted, and previous 

 work (4) has indicated that ultraviolet treatment stabilizes the 

 adapted state. 



The data obtained with the mass spectrometer and summarized 

 in Table I give no reliable evidence for the existence of a true photo- 

 reduction in normal, adapted algae. They indicate that the photo- 

 chemical activity of these algae is mainly, if not completely, photo- 

 synthetic. Nonetheless, since the measurements with the mass 

 spectrometer were, of necessity, made in the presence of appreciable 

 amounts of oxygen (0.04% to 0.24%), and oxygen tension could 

 easily be an important variable in determining the extent of photore- 

 duction, it was desirable to check for the presence of a true photo- 



