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



The cultures were used for the experiments in the present work after 2-10 days 

 growth, when they contained 200-1000 fA cells, depending upon the amount of initial 

 inoculation. Usually 50-100 [x\ cells per 200 ml medium were employed as inoculum, 

 grown as just indicated. Bacterial growth during either cell culturing or manometric 

 experiments was found with a haemocytometer to be negligible, due to the low pn, the 

 lack of added organic matter in the synthetic medium, and possible antibiotics produced 

 by the Chlorella. 



The cells for experimental use were centrifuged in an International No. 2 Centrifuge 

 at the lowest possible speed giving nearly complete settling in 10 minutes and were 

 taken up, with or without further washing, in fresh nutrient medium at a concentration 

 of 30-50 /u,\ cells per ml. 



II. MONOCHROMATOR 



A Steinheil glass 3-prism spectrograph operated with a focal length of 195 mm at 

 F 3.5 for the collimator and a focal length of 710 mm for the telescope was used as a 

 monochromator. The slit was illuminated with a 750-watt projection lamp. The image 

 of the coiled filament at about 20° to its plane was projected onto the slit with an 

 auxiliary lens. A looo-watt voltage regulator was used to supply power to the lamp 

 which operated at constant current. 



The width of the entrance slit was about 2 mm, corresponding to about 20 m/ti in 

 the red. A slit was placed in the focal plane of the telescope and was adjusted to have 

 a width of about 30 m/t covering the region 630 to 660 m/i. A lens was placed behind 

 this slit to throw, in a weakly convergent beam, an image of the exit prism face on the 

 bottom of the manometer vessel. 



The area of the beam at the vessel was about 3 cm^ and the energy flux was about 

 0.6 micro einsteins/min. This intensity was decreased when desired by placing in the 

 light beam, just before the exit slit, blackened wire screens calibrated by the National 

 Bureau of Standards. 



III. MEASUREMENT OF LIGHT ENERGY 



The energy of the light beam was measured by the recently developed chemical 

 actinometer^ whereby for each quantum of visible light absorbed one molecule of Og 

 is consumed. In the same or similar rectangular vessel as used for theyield determinations 

 were placed 2 mg ethyl chlorophyllide, 200 mg thiourea, 7 ml pyridine, and O2 gas. 

 The actinometer vessel was shaken in the thermostat at 20° C in the same manner and 

 in the same cross-section of the light beam as the vessels with the cell suspensions were 

 shaken during the yield determination. The total intensity of light, absorbed by the 

 actinometer, should not exceed 0.3 microeinsteins per minute under our working con- 

 ditions. Higher intensities, as used for the yield determinations, were diminished for 

 this purpose by the calibrated screens. Several 10 minute periods were observed for 

 every actinometer determination. When in t minutes the pressure change in the actino- 

 meter vessel is hog mm, the total energy flux in the light beam in t minutes is — 



or — - microeinsteins (micromole quanta), where the vessel constant kog is expressed 

 References p. 346. 



