368 RESPIRATORY METABOLISM 



normal termites, under anaerobic conditions. However, this gas was not 

 evolved if the intestinal flagellates had been removed by oxygenation, 

 and it was suggested that it might have been evolved by the flagellates. 

 The evidence is incomplete, however, in that oxygenation probably also 

 changed the bacterial flora. Witte (1933) observed the production of 

 gas bubbles by Trichomonas foetus. This was confirmed by Andrews and 

 von Brand (1938), who found that this gas was not absorbable by 

 alkali and that when mixed with O2 it burned with indications of ex- 

 plosiveness. Final identification was not made. The formation of gas 

 vacuoles has been reported for several organisms, but in most cases there 

 is little evidence regarding the identity of the gas. Bles (1929) believed 

 that the gas vacuoles of Arcella contained Oo. 



The chlorophyll-bearing flagellates, of course, might give off Og in 

 the presence of strong light, because of photosynthesis, and this might 

 also be true of the ciliates which harbor zoochlorellae. There is con- 

 siderable indirect evidence that this is true, but no direct measurements 

 are available. 



Investigations Which Concern the Source of Energy 



Whenever an oxidizable material is subjected to complete combustion, 

 the ratio of COg given off to Oo consumed will vary with the type of 

 material. This ratio (COg/Oo) is called the respiratory quotient (R.Q.). 

 Carbohydrates (relatively rich in oxygen) have an R.Q. of 1.0; fats 

 (relatively poor in oxygen) have an R.Q. of about 0.71; and proteins 

 have an R.Q. of 0.83 if the nitrogen is eliminated as urea, and 0.93 if it 

 is eliminated as ammonia. By measurements of the respiratory quotient 

 we may obtain an index of the type of material which is being oxidized 

 by the organism, at least as to whether it is predominantly carbohydrate 

 or predominantly fat. If the excreted nitrogenous material can be identi- 

 fied and measured, the amount of protein and consequently the amounts 

 of carbohydrates and fats consumed can be calculated. Under these con- 

 ditions the measurement of R.Q. becomes more significant. 



These interpretations are based on the assumptions that complete 

 oxidation of metabolic substrates is the sole cause of gaseous exchange, 

 and that gases other than Oo and CO, are not involved. If these assump- 

 tions are unsound, then any interpretation of the R.Q. is necessarily 

 more difficult. If carbohydrate is being converted into fat within the 



