786 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Iron-bacteria.* — Bacteria which assume a nist-colourccl hue were 

 dcnoiiuiiiited iron-bacteria by Ehrenberg, who found that this coloration 

 was clue to the presence of compounds of iron oxide deposited in the 

 Bubstance of the jelly, and regularly distributed. The exact significance 

 of this deposition of iron and the conditions under which it is called 

 forth, are at jirescnt probleniatical. According to one view, that of Cohn, 

 the brown coloration is duo to the deposition of iron oxide by the 

 vegetative activity of the cells, just like silex in diatoms or carbonate of 

 lime in the cell-membrane of Melobesiacete. The other view is that the 

 process is purely mechanical, and is effected by the deposition of iron 

 compounds dissolved in water in tlie gelatinous parts. 



To ascertain which and how far either of these views were correct, 

 Herr S. AVinogradsky made experiments chiefly with Leptothrix ochracea 

 Ktz. 



(1) "When finely-powdered iron oxide was placed in water containing 

 colourless Leptothrix, no brown staining was produced ; but directly 

 water containing carbonate of iron in solution (Pyrmont, Schwalbach) was 

 used, in 10-15 hours a yellowish-brown colour appeared. 



(2) The co-operation of the living plasma is shown by the fact that 

 where the brown coloration is produced, there is no deposit of iron 

 oxide in the immediate vicinity ; consequently the effect is not due to the 

 action of the oxygen in the air. Moreover, the sheaths are only stained 

 when the cells are alive. 



(3) Without the presence of iron oxide, Leptothrix ochracea does not 

 grow. This is clearly shown by changing the fluids ; when the water 

 contains no iron the threads stop their development, but directly it is 

 added growth proceeds again. 



(4) The oxidation process is therefore as follows: — The salts of the 

 oxide of iron are eagerly taken up by the cells, oxidized in the 

 protoplasm, and the compounds formed excreted by the cells. These 

 compounds are soluble ; and after twenty-four hours the colour may 

 usually be removed by washing the threads in water, especially if it 

 contain CO2. Very dilute acids seem to remove the brown hue ^most 

 efficaciously, but are not always successful. 



(5) Leptothrix ochracea can grow in water which contains very little 

 organic matter, e, g. the natural ferruginous waters. The addition of 

 0-005-0 -01 per cent, butyrate of lime or acetate of soda to Strasburg 

 water sufficed to make this bacterium grow well. 



The author does not draw any conclusion from the foregoing experi- 

 ments, except that the oxidizing power of the cells of iron-bacteria 

 must be extremely great, but promises a more complete account in 

 some future publication. 



Bacillus muralis. — Prof. A. Tomaschek,t in reply to Prof. A. Hans- 

 girg, who identifies Bacillus muralis with Glaucothrix gracillima Zopf,| 

 points out that the rods in Glaucothrix {Aphanothece caldariorum Eichter) 

 are distinctly green, while those of B. muralis consist of a plasma which 

 is perfectly homogeneous and almost transparent. The author then pro- 

 ceeds to call attention to the endogenous spore-formation of B. muralis. 

 The commencement of this process is indicated by a number of strongly 

 refracting roundish corpuscles with a bluish reflex, collecting together 



* Bot. Ztg., xlvi. (1888) pp. 261-70. 



t Bot. Ceutralbl., xxxiv. (1888) pp. 279-83 (2 figs.). 



j See tbis Journal, ante, pp. 276-7. 



