430 



LIGHT AND LIFE 



* • , - ... "• ■ >. - -t- 



Fig. 5. Engelniann's expeiiment which showed that oxygen production is con- 

 fined to the ilhiminated chloroplast. 



I, Green algae placed in the middle of a suspension of motile bacteria, as ob- 

 served following a period in the dark. Since the bacteria require minute traces 

 of oxygen for motility they are immobilized and randomly distributed in the dark. 



II, Same preparation as in I following brief illumination. 



III, A^Spirogyra cell illuminated in two different locations. The bacteria con- 

 gregate only where the chlorophyll is illuminated. 



[Prom Plant Physiology, by W. Benecke, and L. Jost, \'olume I. p. 17."). Gusta. 

 Fischer, Jena, 1924.] 



Keilin, in his study of the function of the cytochrome system 

 in respiration, found that the oxidation of cytochrome c and the re- 

 duction of oxygen was inhibited by cyanide, while the reduction of 

 cytochrome c was inhibited by urethane. The production of oxygen 

 in the chloroplast reaction is not affected by cyanide but is very 

 sensitive to urethane. This latter fact indicates the importance of 

 (H) transfer in photosynthesis, a point first emphasized many years 

 ago by van Niel (14) . He used the concept of (H) transfer to give 

 a general explanation for all photosynthetic processes; the produc- 

 tion of the oxygen molecule in photosynthesis was regarded as a 

 special case of light-induced (H) transfer. 



The light-induced (H) transfer in photosynthesis, which is generally 

 represented by Equation ^, may be regarded as being opposite to 

 the thermochemical gradient, a suggestion that may be illustrated by 

 a very simple experiment. Basically this experiment consists of mix- 

 ing together chloroplasts, mitochondria, a crude green-leaf juice, and 

 air. Observation of such a mixture with a low dispersion spectroscope 

 shows that cytochrome r becomes reduced in the light and oxidized in 

 the dark. The light-dark reduction and oxidation of cytochrome c 



