RHODO-THIOBACTERIA 147 



disposition of slime in the cell. A thin layer is formed immediately 

 inside the membrane (Fig. 30A), and, in addition, there are one 

 or two round patches of the same material, either together, or 

 separate. These patches may be situated in any part of the cell 

 (Fig. 31). This organism was found in a pool in Epping Forest, 

 the water of which is periodically coloured a blood-red by it. 

 Usually the red colour appears in autumn, and lasts for a few 

 weeks when the pool again becomes clear and remains so until 

 the f oUowingautumn. The Epping Forest overlies a bed of chalk, 

 so the water is rich in lime. The other microorganisms in the 

 same pond, however, did not appear to have absorbed the lime 

 in any quantity. The richness in the content of lime makes it 

 probable that the organism exercises a selective action in the 



Fig. 30. — Chromatium Linsbaueyi (Gicklhorn). 



A. Appearance of cell in certain conditions after treatment with carbol- 



fuchsin. Immediately behind the membrane is a thin layer of slime 

 which extends round the whole cell inside this membrane. The 

 coloured globules are probably nitrogenous reserve material, and the 

 uncoloured ones lime corpuscles, x 5000. 



B. The same cell unstained and observed " end on." The centre is 



occupied by a large vacuole. All the globules are situated in the 

 peripheral plasma. The globules which appear to occupy the vacuole 

 in this diagram are in reality placed in the plasma on the far side of the 

 cell, which is here viewed " end-on ". x 6000. 



C. The normal [b), and the pleomorphic type (a) of Chromatimn Linsbaueri. 



D. Shows the stages in fission of this species. 



absorption of this substance, but whether it is utilized in its 

 metabolism is not yet ascertained. The cells are ellipsoidal- 

 cylindrical, and measure up to 15/Lt in length and about 6 — 8/x 

 in breadth (Fig. 30). In the natural state, with one exception, 

 no marked deviation from the normal shape was observed. 

 This exception was a spiral form which appeared in some 

 cultures, and was in every other respect similar to the normal 

 organism. This is obviously a pleomorphic form. The 

 dimensions of the " Spirillum " were constant so far as this 

 could be determined from the small number of crude cultures 

 in which it appeared ; and there appeared in this case to be no 

 intermediate forms. The sudden appearance of this pleo- 

 morphic form was not a frequent phenomenon. Sometimes 



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