Introduction 33 



of embryonic cells. Since Cancer cells contain less catalase than normal cells, and 

 since hydrogen peroxide is produced in aqueous Solutions lipon irradiation with x- 

 rays, the obvious explanation was to regard the effect of x-rays on metabolism as a 

 process of hydrogen peroxide poisoning. 



In order to test this theory we developed the manometric x-ray actinometer 

 (analogous to our actinometer for visible light), in which the test cells are first shaken 

 and then irradiated and in which a Fricke's Solution of ferrous sulfate is subse- 

 quently shaken and irradiated under the same conditions. As a result of the radi- 

 ation, ferrous iron is transformed into ferric iron. If, in addition to making the 

 metabolic determination, one assays the amount of iron oxidized in each experi- 

 ment, the effective x-ray dosage becomes known in each instance, regardless of 

 complicated geometrical conditions. 



In order to find the connection between the radiation effect and hydrogen perox- 

 ide, we added catalase to the cells during irradiation; this proved to diminish 

 the radiation effect. Or, better still, we irradiated the Solutions without the cells, 

 then added catalase to the irradiated Solutions, and then added the cells. We found 

 that the irradiated Solutions lowered the fermentation of Cancer cells almost like 

 irradiation; after the addition of catalase, however, the irradiated Solutions no 

 longer affected the fermentation of Cancer cells. 



Studies of this kind, which were extended to the formation of methemoglobin 

 by x-rays showed that it is essentially the hydrogen peroxide formed that inhibits 

 the fermentation of dilute suspensions of Cancer cells during irradiation, rather 

 than the H atoms and OH radicals, which, according to Joseph Weiss, are the 

 primary degradation products of water. Thus, the reactions in which hydrogen 

 peroxide is formed during irradiation 



2 OH = H2O2 

 2 H + 2 = H2O2 



obviously proceed more rapidly under our experimental conditions than do reac- 

 tions of H and OH with fermentation enzymes (60, 63, 64, 65, 66, 82). 



XI. Photosynthesis* 



1. Experimental material 



We no longer use continuous light to cultivate Chlorella for yield determinations ; 

 since 1956, we have used fluctuating light, whose light-dark time intervals corre- 

 spond to the day, night, and twilight periods. This, above all, but also other meas- 

 ures are responsible for the fact that good quantum yields are now reproducible 

 any time at will, and explains failures in earlier times. 



* 1961 Addition. In 1960 "Problems in Photosynthesis" by W. Bladergroen 

 was published in the American Lecture Series (Charles C Thomas, Publisher, 

 Springfield, 111.). This is the first constructive presentation of this field of investi- 

 gations that has appeared in many decades. It does not detail theories but describes 

 experiments and techniques. 



3 Warburg, Zellphysiologie 



