168 A MANUAL OF BACTERIOLOGY 



quantity that the whole marshes and ponds may be 

 coloured blood-red by them/ B. roseo-persicina con- 

 tains dark-coloured sulphur granules, the dark 

 colour being due to the pigment bacterio-purpurin 

 formed by the microbe. This pigment is in- 

 soluble in water, alcohol, etc., and when examined 

 spectroscopically it shows a strong absorption band 

 in the yellow, a weaker band in the green and blue, 

 and a darkening in the more refrangible half of the 

 spectrum. 



Beggiatoa alba. This bacillus occurs as threads 

 without distinct articulations. The threads are 

 longer and thicker than leptothrix, and they are 

 found in marshes and sulphur springs. The cells 

 (about 3*5 Abroad) of B.alba contain sulphur granules 

 (Fig. 33, 20), and, according to Cohn and Cramer, 1 

 these granules consist of crystalline sulphur, which 

 is highly refractive. When these crystalline granules 

 are disintegrated and examined microscopically, 

 they are seen to be composed of a number of 

 rhombic (octahedral) crystals. A variety (B. alba 

 marina) of this microbe forms a delicate white gela- 

 tinous membrane on decaying animals and algae in 

 a marine aquarium. 



Beggiatoa nivea. The threads of this bacillus are 

 very slender, indistinctly jointed, and form undu- 

 lated woolly tufts of milky-white colour. B. nivea 

 occurs in sulphur springs. 



Beggiatoa miralilis. The microbe occurs in sea- 

 water, forming a white gelatinous scum on decom- 

 posing algae, etc. The threads are very thick, 



1 Beitrage zur Biologie der Pfltinzen, vol. i. 



