1911.] 



The Mechanism of Carbon Assimilation. 



105 



2. The Evolution of Oxygen. 



(a) In Vitro. — A method of showing the evolution of oxygen from 

 chlorophyll films in contact with catalase, different from that previously 

 described, has been devised by making use of Beijerinck's luminous bacteria. 

 A pure culture of these bacteria has been observed to glow only in the 

 presence of free oxygen. The experiment, which is described below, can be 

 easily repeated, and involves no troublesome manipulation. The smaller 

 part of a glass Petri dish was divided into two compartments by cementing 

 a narrow strip of cork across the middle. A culture of luminous bacteria 

 in nutrient gelatine was poured into one compartment, and part of the same 

 culture containing some sheep's liver catalase into the other. When the 

 gelatine was set, a film of chlorophyll was painted evenly over both halves, 

 and the lid was put on. The cell was then sealed by pouring melted 

 paraffin wax into the annular space between the rims of the dish and its 

 cover, and gold size was then poured round on top of the wax, by which 

 means the cell was made quite air-tight. It was placed now in a dark room, 

 and both halves were seen to glow with equal brightness, which gradually 

 diminished as the oxygen in the imprisoned air was used up. After two 

 days, no glow could be detected in either half, even after 15 minutes' 

 examination in the dark room. At this stage the cell was taken out and 

 exposed to light for five minutes, and then brought back to the observer in 

 the dark room, when both halves were seen to be feebly glowing, but with 

 unequal brightness. When this glow had again ceased, the experiment was 

 repeated with a different observer, and with the same result. On comparing 

 notes, it was found that each observer had noticed a somewhat brighter 

 glow in the half which contained no catalase. This result was unexpected, 

 but it was subsequently found that the bacteria could be made to glow much 

 more brightly by adding a drop of very dilute hydrogen peroxide than by 

 simply exposing them to atmospheric oxygen, that is to say, they are them- 

 selves able to utilise hydrogen peroxide for the light-producing process, and 

 in doing so derive more energy from it than from a direct supply of gaseous 

 oxygen. This experiment therefore not only shows the production of oxygen 

 under the conditions named, but further supports the view that this oxygen 

 is derived from hydrogen peroxide. 



(b) In the Plant. — The distinction between the behaviour of a plant which 

 had been chloroformed, i.e. in which the enzymes had not been destroyed, 

 and that of one in which both protoplasm and enzymes had been killed by 

 immersion in boiling water, was emphasised in Part I, and since more than 

 one writer has failed to confirm the observation therein recorded, that a 



