240 SELMAN A. WAKSMAN AND J. S. JOFFE 



The media were distributed in 100 cc. portions into 250 cc. 

 Erlenmeyer flasks and sterilized in flowing steam, for 30 minutes, 

 on three consecutive days. The flasks were then inoculated 

 with various dilutions of the composts. ]\ledium 2 was found 

 to allow a growth of both a sulfur oxidizing bacterium and one 

 or more species of fungi. By omitting the glucose from the 

 medium, the fungi were practically ehminated. 



It was found later that, by cutting down the tri-calcium 

 phosphate in the medium to 0.25 per cent, a more rapid develop- 

 ment of the organism took place, thus giving medium 3, which 

 is a modification of 1 and 2. 



Well advanced composts were used for inoculation. The 

 material was diluted 10, 1000, 100,000 and 10,000,000 times 

 with sterile water, then 1 cc. of each dilution was added to 100 

 cc. of the sterile medium and the flasks incubated, at 25°, for 

 seven to fourteen days. 



The flasks became turbid on the fourth or fifth day, the amount 

 of turbidity depending upon the dilutions used, the higher 

 dilutions developing slower than the lower ones. A pellicle or 

 fungus mycelium was formed only in the flasks containing 

 glucose. By transferring the cultures into fresh flasks, the 

 same phenomenon was observed A\'ith a uniform turbidity in 

 four to five days. By examining the culture under the micro- 

 scope, it was found to contain a very minute non-motile bacterium 

 present in abundance and accompanied by a few larger cylindri- 

 cal cells which were found to be spores of a fungus occurring 

 abundantly in the compost. The impure culture of the or- 

 ganisms was found to possess strong sulfur-oxidizing properties, 

 about 200 to 300 mgm. of the sulfur being oxidized, in each 

 flask, in fourteen days. In the presence of tri-calcium phosphate 

 more of the sulfur is oxidized, since the acid formed is used up in 

 converting the insoluble phosphate into soluble calciimi-acid- 

 phosphate and calcium sulfate. A further accumulation of the 

 sulfuric acid resulted also in the formation of phosphoric acid 

 and calcium sulfate. The medium had originally a reaction 

 equivalent to pH 5.6 to 6.2. Following the oxidation of the 

 sulfur, the reaction became gradually acid and, at a pH of 



