236 SELMAN A. WAKSMAN 



Na2HP04, 0.2 to 1 per cent Na2S203 and some JVIgCOj, he ob- 

 tained a good growth of these bacteria and, on adding agar, he 

 has been able to isolate them in pure culture. In the absence of 

 the carbonate, but in the presence of CO2 containing air, the 

 growth was much slower; in the absence of both carbonate and 

 CO2, no growth took place, even in the presence of various organic 

 substances. The medium did not become acid even in the ab- 

 sence of carbonate, indicating that the oxidation of the thiosul- 

 fate did not take place according to the formula : 



Na2S203 + H2O + 40 = NajSOi + H2SO4. 



but according to the following reaction: 



" 3Na2S203 + 50 = 2Na2S04 + Na2S406. 



While no sulfur accumulates within the cell, there is an abundant 

 production of free sulfur outside of the cell, not in direct contact 

 with the colony, but at some distance from it, suggesting an extra- 

 cellular oxidation. 



Beijerinck (1904) confirmed the results of Nathanson (1903) 

 by the use of a medium consisting of 100 parts of water, 0.5 

 NasSjOs. 5H2O,0.1NaHCO3, O.O2K2HPO4, 0.01 NH4CI and 0.01 

 part MgCU. The medium was not sterihzed, was inoculated 

 with canal water and incubated at 28 to 30°. In 2 to 3 days, the 

 surface of the medium became covered with free sulfur, filled with 

 bacteria. On making a transfer into a fresh flask with medium, 

 a suKur layer was obtained in 24 hours. According to Beijerinck 

 (1904), the reaction takes place as follows: 



Na2S203 + O = Na2S04 + S. 



This reaction is exothermic and functions as a source of energy, 

 which is used for the reduction of NaHCOa and for the building 

 of the bacterial body. CaS and HoS can replace the thiosulfate. 

 H2S+O = H2O +S. 



Nan S4 Os + Na2 CO3 + = 2 Na2S04 + CO2 + S2 



The ammonium salt can be replaced by nitrates. No other of 

 the organic substances tested could replace the carbonic acid as 



