Further researches concerning oligonitropholous 



microbes. 



Proceedings of the Section of Sciences, Kon. Akademie van Wetenschappen, Amster- 

 dam, Vol. IV, 1902, p. 59. Verscheen onder den titel Verdere onderzoekingen 

 over oligonitrophile Mikroben in Verslagen Kon. Akademie van Wetenschappen, Wis- 

 en Natuurk. Afd., Amsterdam, Decl X, 1902, biz. 8 13. 



In my first paper on oligonitrophilous microbes 1 ) I still left the question unanswered 

 after the forms which develop in the light, in nutrient liquids, which only 

 contain traces of nitrogen compounds, and whose nutrition with carbon can only be 

 effected from the carbonic acid of the air. 



The experiments to answer this question were made as follows. Large flasks 

 were plugged with cotton wool or filtering paper, so that the air has free access, or 

 closed in such a way that the air could be renewed, and that, at each renewing, it 

 must pass through strong sulphuric acid in order to be deprived of the nitrogen- 

 compounds. These flasks had been half filled with 



100 Tap- or distilled water 



0.02 K-HPO 4 

 and infected with a not too slight quantity of garden-soil, e. g. I to 2 grs. per liter"). 



They were placed in winter at a window on the south, in spring and in 

 summer on the north-west, and in the beginning they were now and then shaken, in 

 order to sink the floating film of calciumphosphate, which forms at the surface. 



As the rate of nitrogen and carbon compounds is too slight to cause any 

 appreciable development of colourless microbes, no further cloudiness results, but 

 that of the easily precipitating phosphate. But in winter after six to eight, in 

 summer after four to five weeks, a characteristic flora develops consisting of some species 

 of Cyanophyceae, which, once become visible, can promptly give rise to a deep bluish- 

 green colouring of the liquid. In the beginning these Cyanophyceae are seen to 

 develop as free colonies at the sides of the flask, later there also appear floating 

 films, which latter consist chiefly of Anabaena, while among the colonies growing on 

 the glass-wall, not only the large flat colonies of Anabaena, but likewise the charac- 

 teristic, but rarer bluish-grey slimy lumps of Nostoc paludosum are most striking. A 



') These Proceedings of March 30, 1901. 



' 2 ) The Delft tap-water contains a present 0.42 mG. nitrogen per L., the garden- 

 soil used 0.56 pCt. nitrogen (analyses of Mr. A. v. Del den); but this nitrogen can 

 only for a minimal portion (as ammonia and nitrate-nitrogen) be assimilated by mi- 

 crobes. The oligonitrophili themselves posses the specific faculty of feeding on the 

 nitrogen from the atmosphere. 



