PRODUCTION OF HYDROGEN PEROXIDE 159 



light. They also describe an experiment to show that a 

 parallel result is obtained in vitro. 



A Petri dish is divided into two by a strip of cork 

 cemented across the middle. A culture of luminous bacteria — 

 which are extraordinarily sensitive to free oxygen and glow 

 only in its presence — in nutrient gelatine was poured into one 

 compartment, and in the other was placed the same culture but 

 with catalase added. When the gelatine was set, a film of 

 chlorophyll was painted over the surface. The lid was then put 

 on and firmly fixed with wax and gold size in order to make 

 the joint quite air-tight. The preparation was then placed in a 

 dark room. After the lapse of two days no glow was dis- 

 cernible. The dish was then exposed to daylight for five 

 minutes, and once more examined by the observer in the dark 

 room. The bacteria were found to be glowing, the side con- 

 taining no catalase showing the most light, a difference which 

 at first sight is surprising, but it was found that the bacteria 

 would glow in the presence of very small quantities of hy- 

 drogen peroxide. 



There is another point of considerable importance. The 

 formation of formaldehyde and hydrogen peroxide from car- 

 bonic acid involves the absorption of heat, so that a film of 

 chlorophyll placed in an atmosphere containing moist carbon 

 dioxide should, when illuminated, be at a lower temperature 

 than a control film in an atmosphere free from carbon dioxide. 

 By the use of a thermo-junction and a suspended coil galvan- 

 ometer this was found to be the case. 



Some of the earlier experiments and conclusions arrived 

 at by Usher and Priestly have been adversely criticized by 

 Blackman * and Ewart f ; their later work, however, places 

 their conclusions on a much firmer basis. 



Ewart's conclusion that chlorophyll contains formaldehyde 

 in a combined state has been confirmed by Schryver,J who has 

 published certain observations on the subject. He finds 

 that formaldehyde is more abundant in chlorophyll films 

 after exposure to bright sunlight than when exposed to a dull 

 light. He also states that if glass plates covered with films of 



* Blackman : " New Phytol.," 1906, 5, 132. 



+ Ewart: " Proc. Roy. Soc, Lond.," B., 1908, 80, 30. 



X Schryver : " Proc. Roy. Soc, Lond.," B., 1910, 82, 226. 



