ANAEROBIC BACTERIA 177 



of a number of other gases. It is sufficient to mention hydrogen and 

 methane, as a result of decomposition of carbohydrates, hydrogen sul- 

 fide as a result of reduction of sulfates, elementary nitrogen and oxides 

 of nitrogen as a result of reduction of nitrates, and various amines, 

 elementary nitrogen and oxides of nitrogen, hydrogen sulfide, mercap- 

 tans and thioether as a result of decomposition of proteins. It is neces- 

 sary to be able to measure these and determine them quantitatively, 

 especially since they are often of great economic importance when a soil 

 is water-logged for a longer or shorter period of time. The bacteria 

 are grown on suitable media (specific for the various organisms) 

 under anaerobic conditions, in tubes or bottles connected with a manom- 

 eter. The tubes may also be placed in a Novy jar used as a respiratory 

 chamber. 77 The growth may be carried on in an atmosphere of pure 

 gas, such as N 2 , H 2 , C0 2 . By using a compensation manometer, the 

 pressure changes taking place within the culture tube or jar can be 

 observed constantly, these changes indicating the periods of active 

 growth followed by the cessation of growth and respiration. The 

 samples of gas are withdrawn directly into a burette or first into a 

 sampler, then into a modified Henderson-Haldane or other suitable 

 apparatus. 



The volume of the gas to be analyzed is first measured; the gas is 

 then passed back and forth into 10 per cent KOH solution to absorb the 

 C0 2 , which is determined by difference in the volume of gas. The latter, 

 freed from C0 2 , is passed into an alkaline pyrogallate solution (or 

 sticks of yellow phosphorus in water) to absorb the oxygen; the latter 

 is determined also by the difference in volume of the gases. The 

 estimation of hydrogen, methane and other combustible gases is carried 

 on in a combustion chamber over heated platinum, in the presence of 

 oxygen (or air as a source of oxygen). By measuring the amount of 

 C0 2 formed in combustion, it is possible to calculate the amount of 

 methane and other hydrocarbons present in the gas mixture; the amount 

 of hydrogen is then determined by the difference between the loss due 

 to combustion and the methane present. The amount of oxygen 

 absorbed in the combustion is obtained by calculation or by the differ- 

 ence between the oxygen added and that remaining, as determined by 

 absorption in the pyrogallate solution. The C0 2 present in the medium 

 (liquid) is aerated into standard Ba(OH) 2 solution, then titrated. 



77 Novy, F. G., Roehm, H. R., and Soule, M. H. Microbic respiration. I. 

 The compensation manometer and other means for the study of microbic respira- 

 tion. Jour. Inf. Dis. 36: 109-167. 1925. 



