THE CULTURE OF THE SULPHUR BACTERIA 



63 



the vessels containing decomposing seaweed show a much 

 stronger growth of the purple organism when stoppered. 

 The growth of the organism is hkewise m.uch better in pools 

 or in cultures in w hich the sulphuretted hydrogen is enough to 

 cause a perceptible smell. Finally, active growth follows ex- 

 posure to subdued light, but does not take place in the dark or 

 when exposed to bright light. Dr. Blodwen Lloyd, in the 

 author's laboratory, has succeeded in cultivating Thioporphyra 

 in a medium made up of potassium nitrate 0-5 gram, sodium 

 dihydric phosphate 0-25 gram, calcium malate 5 grams, and 

 sea water lOOO cc. The nitrogen in this culture was thus 

 obtained from the nitrate, and the carbon almost certainly 

 from the CO2 of the atmosphere. On further cultivation, 

 however, the size of the organism rapidly diminished in this 

 artificial medium, probably because the nitrate was not the 

 best source of nitrogen. So far as the investigation has pro- 

 ceeded, the results confirm those obtained by Keil, Skene, and 

 Bavendamm, but it is not yet known whether under natural 

 conditions nitrogen is derived, as Molisch believes, from organic 

 matter, or, as Skene thinks, from products resulting from the 

 decomposition of organic matter. 



Changes Effected in the Constitution of the Water 

 BY Thioporphyra volutans 



The chemical changes which take place in a marine pool 

 during the growth of Thioporphyra volutans have been investi- 

 gated (Ellis and Stoddart). An analysis of the water of a 

 neighbouring marine pool in which there was no decomposing 

 matter is given for comparison in the following table : — 



A pool containing decomposing matter was kept under 

 observation for ten weeks during the summer, and samples of 



