184 



Also on silica plates, prepared in glass dishes, which, after extraction of the 

 chlorides are soaked with a nutrient solution, B. oligocarbophilus can produce very 

 fine cultures, appearing after some weeks, as snowwhite colonies with indented mar- 

 gin, and which by a right selection of the salts, can finally spread over the whole plate. 

 Then the remarkable phenomenon is observed, that the silica liquefies a little in the 

 centre of the colonies and sinks in by evaporation. 



The silica plates are made as follows. A commercial solution of potassium silicate, 

 diluted with a known quantity of water, is titrated with normal hydrochloric acid. As 

 the solidification is much favoured by an alkaline reaction, a complete neutralisation 

 at the preparation of the plate should not occur, and as a plate, with a high percent- 

 age of silica, contracts strongly after coagulation, and expresses much water, the 

 dilution must be sufficient for this contraction to be delayed. Into a small beaker-glass 

 was introduced, in a certain case, 5 cM 3 of potassium silicate diluted with 25 cM 3 of 

 water, and into a second glass the required quantity of hydrochloric acid, amounting 

 to 10 cM 3 of normal acid. The acid is mixed with the diluted silicate and the mixture 

 poured into a glass dish. The solidification delays the longer as the mass is more 

 diluted, but it is easy, after some practice, to make very solid plates. The plate is first 

 freed from the chlorides by streaming tap-water, then washed out with boiled water, 

 and afterwards treated with the solution of nutrient salts. When these have suffi- 

 ciently diffused into the plate, the glass dish is gently warmed at the underside, until 

 the adhering water has evaporated and the plate shows a dry, glossy surface. The 

 surface is flamed in the B u n s e n-burner, by which only a partly but sufficient sterili- 

 sation is to be attained. 



Not only B. oligocarbophilus, but also the ferments of nitrification grow on this 

 medium very well. By mixing of the diluted solution of the silicate with chalk, mag- 

 nesium carbonate, or ammonium-magnesium phosphate, snow-white plates may be ob- 

 tained, which are particularly fit for the culture as well of all these microbes as of 

 several lower algae. Even earth-diatoms, of the genus Nitsschia will grow thereon. 



Once more it must be observed, that in the silica plates organic substances must 

 be absent, even fragments of cork, fallen into the silicate solution, may disturb the 

 experiment. 



The pure cultures, obtained on agar or silica plates, are as well fit for the furtht-r 

 experiments on liquid media as the crude cultures, of which many experiments, con- 

 tinued for years, have convinced us. Every thought of symbiotic relations on which 

 the carbon assimilation by our bacterium might repose is thereby excluded, so that at 

 least the biological side of this part of our problem is clear. 



Concerning the further properties of our bacterium in pure cultures, we can be 

 brief. In the films, as well as on in the colonies on the solid media, it consists of 

 minute, thin and short rodlets, probably always immobile. They are ca. 0.5 ju wide and 

 -4 (n long. The length however is very variable and frequently particles are seen 

 0.5^1 wide and 0.7 i JLI Ion?. Often, when not using reagents, such as dyeing sub- 

 stances or acids, no structure at all is to be observed, neither in the colonies nor in the 

 flowing pellicle, but the bacteria at once become visible by staining the preparations. 

 The thick cellwalls form the chief constituent of the colonies: albuminous matter is 

 only present in a slight quantity in this bacterium. 



