Physiology of the Purple Sulphur Bacteria. 
none. If in addition we use boiled air-free water, and seal the 
flasks with liquid paraffin, the result is exactly the same—no 
development occurs. 
It was thought possible that the hydrogen sulphide might be 
replaced by sodium thiosulphate. The following scheme was 
carried out:— 
0-5% Sodium thiosulphate. 
+ the usual salts 
v + 1% Potassium nitrate- 
All cultures gave a negative result. 
Finally I tried a number of other sulphur compounds, to see if 
it were at all possible to replace the hydrogen sulphide:— 
Sodium bisulphite. 
Sodium sulphide. 
Sodium thiosulphate. 
Potassium sulphide. 
Calcium sulphide. 
Iron sulphide. 
Of each 05% was added to the culture solution, and four 
different conditions were investigated :— 
A a. Aerobic. 
A b. Anaerobic (boiled water + paraffin). 
B a. + 05% Potassium nitrate, aerobic. 
B b. + 0-5% Potassium nitrate, anaerobic. 
A few bubbles of hydrogen sulphide were added to each that the 
change might not be too sharp. 
The results were throughout negative 1 ; even after six weeks no 
trace of development was visible. The material that was used for 
infection gave a fine growth in a fortnight (August) under suitable 
conditions. 
It may therefore be concluded with certainty, that the presence 
of a certain amount of hydrogen sulphide is absolutely necessary to 
the development of the purple sulphur bacteria. 
1 In one anaerobic thiosulphate culture a purple sulphur bacterium, which 
does not agree with any of Winogradsky’s forms, appeared : it seems to come 
nearest Rliabdochromatium : the cause of this requires further investigation : 
there is the possibility of a production of hydrogen sulphide by reduction of 
the ammonium sulphate. 
