PHYSIOLOGY OF THE SULPHUR BACTERIA 283 



ground of the concordant results yielded in separate instances by chemical 

 reactions, a few of which are now given. The pigment is insoluble in water or 

 ether, but is soluble in cold alcohol (as found by Winogradsky in contradiction of 

 Lankester's report). It is converted, by warming with water and by chloroform, 

 into a golden-brown compound, which is changed into brown by hot alcohol, 

 hydrochloric acid or acetic acid ; whereas ammonia or caustic potash produces 

 no visible change at first, but finally gradually develops a dirty shade of colour. 

 Concentrated sulphuric acid changes the red almost instantly into a deep blue ; 

 which afterwards gradually tones into a brownish green. This reaction resembles 

 that set up by the same acid with the lipochromes. Bacterio-purpurin is very 

 quickly destroyed by oxidising agents (e.g. dilute nitric acid or bromine water). 

 Iron and manganese appear to favour its production, a conclusion deduced from 

 the fact that the addition of the protosulphide of either of these rnetals to the 

 medium results in a much stronger coloration of the cells. The sensitiveness 

 of bacterio-purpurin to chemical influences explains the varied change of tone 

 produced in the colour in one and the same cell under different external 

 conditions, causing it to assume all shades, from pure violet to purple, peach- 

 blossom red, rose, orange, brown-red, and brown. With regard to the spectrum 

 of bacterio-purpurin, examined by Lankester, Warming, and Englemann, details 

 have already been given in 92. 



The classification of the non-filamentous sulphur bacteria, drawn up by 

 Winogradsky and briefly outlined above, received an important extension by 

 M. JEGUKOW'S (III.) discovery that, in addition to the red species already 

 described, certain colourless non-filamentous sulphur bacteria also occur in 

 Nature. Two of these he subjected to a closer physiological examination, which 

 will be referred to in the succeeding paragraph. The one of them, indicated as 

 species a, occurs as slightly curved motile rods, their breadth varying from 1.4 

 to 2.3 /JL, and the length between 4.5 and 9 /it. For the second species, known 

 as /3, the dimensions are 0.6-0.8 /z and 2.5-5 P- respectively. 



202. Physiology of the Sulphur Bacteria. 



The true nature of the rounded, highly refractive enclosures present in these 

 fission fungi, and attracting the eye of the microscopist, was first recognised by 

 Cramer, whose discoveries are noticed in a treatise by C. MULLER (I.). It was 

 shown in these experiments that these granules behaved exactly like sulphur in 

 presence of solvents, and they were therefore thought to consist of that element. 

 F. COHN'S (II.) extension of these investigations (which were confined to 

 Heggiatoa, and were confirmed by J. Mayer-Ahrens) to the red sulphur bacteria 

 as well, led to the same result : the granules appearing in these coloured 

 Schizomycetes, under certain as yet undefined conditions, are composed of 

 pure sulphur. The term granules applied to these forms is unsuitable, inasmuch 

 as they consist not of solid granular, but (as Winogradsky afterwards proved) of 

 oily, amorphoiis sulphur, the greater part of which is soluble in CS 2 . However, 

 when the enveloping cells are killed, the sulphur granules are gradually changed 

 into the crystalline modification of this element. If a few Beygiatoa threads 

 rich in these droplets be immersed in concentrated picric acid and left in water, 

 a number of very fine monoclinic prismatic plates and rhombic octahedra will 

 be found in the threads after a lapse of twenty-four hours, and it will at the 

 same time be noticeable that the growing crystals have penetrated the adjacent 

 cell walls. 



F. Cohn was the first to investigate the origin of these internal constituents, 

 which occasionally fill the cell to such an extent as to exceed 90 per cent, of its 

 weight. Starting from the fact that the sulphur bacteria are only found in 



