10 Scientific Proceedings (125) 



the methane, hydrogen and particularly iron bacteria belong to 

 the second group. 



Respiration in the case of autotrophic bacteria is different 

 from that of the heterotrophic forms; it consists in taking in 

 carbon dioxide and giving out oxygen, at the same time con- 

 suming large quantities of oxygen for purposes of oxidation 

 which yields the energy necessary for the activities of the or- 

 ganisms. Meyerhof was the first to demonstrate conclusively 

 that the nitrite and nitrate forming bacteria obtain their carbon 

 only from the carbon dioxide of the atmosphere or in the form 

 of bicarbonate in solution. To demonstrate the carbon assimila- 

 tion by the sulfur-oxidizing organism, Sulfomonas thiooxidans, 

 the following procedure was followed: A medium consisting of 

 0.2 gm. (NH 4 ) 2 S0 4 , 3 gm. KH 2 P0 4 , 0.5 gm. MgS0 4 , 0.25 gm. 

 CaCL, 0.01 gm. FeS0 4 and 10 gm. of elementary sulfur per 

 1000 c.c. of distilled water, placed in 100 c.c. portions in 250 

 c.c. Erlenmeyer flasks was sterilized and inoculated in the usual 

 manner. To some of the flasks 1 per cent, of dextrose was 

 added, or 0.1 per cent, of NaHCO.,, or 0.1 per cent. NaHC0 3 

 N 



and sufficient -y H 3 P0 4 to neutralize the excess alkalinity. The 



flasks were divided into two series; (1) placed in the incubator 

 kept at constant temperature and (2) placed under bell jars, with 

 a carbon-dioxide free atmosphere. The air passing through 

 the jars was drawn through a soda-lime tube and bottles con- 

 taining 50 per cent, solution of KOH. The jars were sealed 

 on to a bench in the same incubator (at 28° C) with the first 

 series of flasks. At the end of 7 days, the hydrogen-ion con- 

 centration and titratable acidity (for 10 c.c.) of the cultures were 

 determined. These serve as an index of the amount of sulfur 

 oxidized. 



