NON-FILAMENTOUS SULPHUK BACTERIA. 369 



occurs in one direction only. The Amoebobacter species are distin- 

 guished by an amoeboid movement; those of Thiodictyon owe 

 their name to the recticular conjugation of their spindle-shaped 

 cells ; whilst Thiopolycoccus forms zoogloea of closely crowded cocci. 

 The genus Thiothece is distinguishable from all other sulphur 

 bacteria by its particularly thick gelatinous sheath. 



A few remarks with regard to the properties of bacterio- 

 purpurin will be opportune in this place. The difficulties in the 

 way of preparing a quantity sufficient for the performance of a 

 chemical analysis have not even yet been overcome ; consequently 

 its chemical composition is still entirely undefined, and we cannot 

 yet say with certainty whether the colouring matter is the same 

 in all red sulphur bacteria. This is, however, assumed to be the 

 case, on the 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 chloro- 

 form, 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 lipo- 

 chromes. Bacterio-purpurin is very quickly destroyed by oxidis- 

 ing 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 metals 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, Warm- 

 ing, and Engelmann, 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. JEGUNOW'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 /*, and the length between 4.5 

 and 9 \L. For the second species, known as /?, the dimensions 

 are 0.6-0.8 p and 2.5-5 P respectively. 



VOL. I. 2 A 



