344 o. WARBURG et al., s. b. hendricks vol. 4 (1950) 



sation point and for short periods of time (minutes), but also with Hght intensities well 

 above the compensation point (several fold), and in experiments lasting many hours. 

 It is important to emphasize that with the same cell suspension the same quantum 

 yields may be obtained both below and far above the compensation point. 



The new results resolve several uncertainties left open by the experiments of 1923. 

 At that time the light intensities were so low that only a fraction of the respiration was 

 compensated by the light. Thus the objection could never have been refuted that light 

 inhibited respiration anticatalytically, that is, without expenditure of energy. But now, 

 in the experiments above the compensation point, this question is eliminated, and 

 chemical energy, corresponding to positive O2 production and CO2 consumption, is in 

 fact clearly gained. 



It was a further shortcoming of the experiments of 1923, that the yields had been 

 determined only for short periods of time [e.g., 10 minutes). But now, in the experiments 

 above the compensation point, the cells are so nearly under their natural culture con- 

 ditions, that there is no evident time limit to yield determinations. Thermodynamically 

 this is a noteworthy advance since the longer the experiments the surer becomes the 

 necessary condition of all calculations of yield: that the absorbed light energy is the 

 sole source of energy for the photosynthetic processes. 



Finally, we may point out that the methodology has been so simplified that effi- 

 ciency determinations can be carried out wherever simple manometric equipment and 

 a suitable light source are available, without the need of a bolometer, thermopile, 

 cathetometer or special differential, manometer. In fact, demonstration of the high 

 quantum efficiencies reported in this paper may readily be made in the laboratory 

 classroom. 



A cknowledgements 



Valuable aid in these experiments was provided by Mrs Lois B. Macri, Mrs Clara 

 F. Smith, and C. R. Newhouser. The culture of Chlorella pyrenoidosa was provided 

 by Dr F. E. Allison of the Plant Industry Station, United States Department of Agricul- 

 ture, Beltsville, Maryland. We wish to thank E. Machlett and Son, New York City, 

 for special facilitation of provision of the manometric glassware, and the American 

 Instrument Company, Silver Spring, Maryland, for the specially adapted thermo- 

 stat and shaking mechanism employed. 



RfiSUMfi ET CONCLUSIONS 



Depuis le developpement des nouvelles methodes et des nouveaux precedes decrits, nous avons 

 trouve, a peu pres sans exception, une efficience de 3 a 5 quanta par molecule d'oxygene produite 



CO 



par raction de la lumiere rouge. Les coefficients ^ observes simultanement pour Taction de la 



lumiere se trouvaient entre — 0.8 et — 1.3, ce qui signifie que I'efficience en quanta pour la lumiere 

 rouge est a peu pres la meme pour la consommation de CO, que pour la production de Oj. 



Ces resultats ont €te obtenus non seulement pour de faibles intensites et de courtes periodes, 

 mais aussi pour des intensites bien au-dessus du point de compensation (plusieurs fois) et pour des 

 experiences durant plusieurs heures. II est interessant de noter que Ton peut obtenir les memes 

 rendements en quanta pour une meme suspension cellulaire au-dessous et au-dessus du point de 

 compensation. 



Les nouveaux resultats resolvent plusieurs incertitudes qui avaient subsistees apres les expe- 

 riences de 1923. A cette epoque, les intensites de lumiere 6taient si faibles que seule une fraction de 



References p. 346. 



