400 Dr. G. S. West and Mr. B. M. Griffiths. [July 7, 



the sulphur globules disappear in about 48 hours, the sulphur being oxidised 

 in the process of respiration. The oxidation of the sulphur can best be 

 demonstrated by allowing a culture to remain undisturbed for several days 

 in a small quantity of water containing minute traces of lime. The organisms 

 gradually lose all their sulphur, and a considerable deposit of granular crystals 

 of calcium sulphate is formed. 



By allowing the bacteria to dry on a slide, and then irrigating with water, 

 the sulphur is obtained in small rhombic crystals (fig. 18). Crystals can also 

 be obtained by allowing the formalin solution in which the bacteria have 

 been fixed to slowly evaporate. These do not appear, however, to be crystals 

 of pure sulphur.* 



From the general behaviour of the sulphur globules, there are many reasons 

 for supposing that the sulphur is not pure, but exists in some kind of loose 

 combination, possibly with proteid material. The crystals obtained by drying 

 the organisms and then irrigating with water are only formed outside the 

 cells. After irrigation the colloidal sulphur, or sulphur-compound, passes 

 through the wall of the cell, without causing the latter any injury, and 

 crystallisation of the sulphur takes place in the surrounding medium. 



Cultures. — Like other sulphur bacteria, Hillhousia will not grow on gelatine 

 or agar.f We have obtained the best cultures in tap water containing minute 

 traces of sulphuretted hydrogen. 



Straining the mud through coarse muslin enables one to obtain almost all 

 the bacteria, mixed only with various small living organisms, finely divided 

 flocculent organic matter, and small sand-grains. The great weight of the 

 bacteria can now be utilised to obtain a pure collection, as it is possible to 

 remove the other organisms by means of a fine pipette, while the large 

 sulphur bacteria and the small sand-grains remain as a sediment. If this 

 sediment be now transferred to a watch-glass it is possible to separate the 

 major portion of the sand-grains by a judicious tapping of the glass while held 

 in a slightly inclined position. In this way the bacterium can be obtained 

 mixed only with very minute sand-grains. We have not yet succeeded in 

 obtaining a culture of the bacterium entirely free from these tiny fragments 

 of silica, although some method of chemotaxis might possibly solve the 



* After several hours' treatment with 40-per-cent. formaiin, the individual bacteria are 

 found to be encrusted with a thick deposit of radiating crystals. On the addition of 

 more water to the solution the crystals are dissolved. If weaker formalin is used, the 

 crystals are never formed, as the substance (some compound of sulphur) is dissolved as 

 fast as it is produced. 



t Winogradsky, in ' Ann. de l'lnstitut Pasteur,' 1889, pp. 49 and 50, has stated his 

 inability to obtain cultures of Beggiatoa, Thiothrix, Chromatium, etc., on solid culture 

 media. 



