272 RADIATION BIOLOGY 



In one type of two-vessel manometric apparatus, the two vessels have 

 the same cross section and the same exposure to Hght, and each is filled 

 with algal suspension to the same depth. One vessel, however, has an 

 extra gas space above the solution to change the (gas volume) /(liquid 

 volume) ratio. In another type the vessels are identical, and the differ- 

 ence in gas/liquid ratio is accompUshed by having the level of the algal 

 suspension different in the two vessels The latter arrangement, how- 

 ever, may give rise to a different amount of light absorption in the two 

 vessels, particularly under the conditions of shaking, and thus lead to an 

 inequality in the gas pressures of the two vessels which is not due to the 

 different sizes. The two vessels containing the algal cells have optically 

 perfect bottoms, through which the beam of light passes into the algal 

 suspension. The hght beams are adjusted until they are equal. The 

 vessels are immersed in a water thermostat and connected to each other 

 by a U-shaped manometer filled with water or other liquid of low density. 

 The vessels and the manometer are shaken vigorously to expose a large 

 surface of liquid to the gas in order to decrease the time required for the 

 attainment of equihbrium. A shaking rate of 150 oscillations per minute 

 and an amplitude of 1 or 2 cm are advocated. 



For many purposes the one-vessel method is superior to the tAvo-vessel 

 one. Differential time lags cannot be magnified to give such large errors, 

 but an independent measurement of the CO2/O2 ratio is necessary if the 

 two gases are involved. In alkaline buffers, where oxygen is the only gas, 

 the single-vessel method is preferred. In some manometers chemicals 

 are inserted in side tubes which maintain either the carbon dioxide or 

 the oxygen at constant pressure. If gas equilibrium is quickly reached, 

 these methods have the advantage of simplicity. They have been sum- 

 marized by Burk, Schade, et al. (1951), who have proposed a three-vessel 

 method. 



A great deal of work has been devoted to the careful analysis of these 

 manometric methods (Tonnelat, 1944) as used in measurements of photo- 

 synthesis, and Emerson and his associates have made an exhaustive study 

 of the problem. The findings are summarized in recent books (Emerson 

 and Nishimura, 1949; Nishimura et al, 1951; Rabinowitch, 1951), and 

 they can be mentioned only briefly here. 



Emerson and Lewis (1939) obtained values for $-1 of 8-10 photons 

 per molecule using the two-vessel manometric method, but were able to 

 duplicate the values of about 4 obtained by Warburg and Negelein (1922, 

 1923) by special adjustment of the conditions. They even obtained a 

 $-1 value of less than 3, which is a theoretical impossibility, indicating 

 that the measurements were not significant. They attributed the diffi- 

 culty to the Emerson carbon dioxide burst, and there is good evidence 

 for this increase of carbon dioxide when darkened algae are first exposed 

 to the light. Loomis (1951) obtained abnormally high pressures due to 



