1 83 



It should, however, be kept in view, that the productivity in bacterial substance, 

 in consequence of the film formation, is not determined by the volume, but chiefly by 

 the extent of the surface of the medium, which is in free contact with the air. Hence, 

 in a very thin layer of tap-water, the nitrogen may soon be consumed, whereas, with 

 the same amount of nutrient liquid, but with a smaller surface, consequently in a 

 thicker layer, the provision of nitrogen will suffice for a longer time. Therefore, in 

 order to obtain from a flask of determined size, the maximum production of B. oligo- 

 carbophilus, a nitrogen compound should be added when a small quantity of tap-water 

 is used, which addition is not necessary when cultivating in a greater quantity in a 

 flask of the same size. 



3. Pure culture. 



Our bacterium does not grow at all or only to a slight extent on the commonly 

 used bacteriological media, these containing too much organic food. But it is easy to 

 produce pure cultures on solid media, when observing the same precautions which I 

 described in the Meeting of the Academy of 27 June 1892 for the pure culture of the 

 ferments of nitrification on agar-plates 1 ), and to which I referred in the Meetings of 

 30 March 1901 (Proceedings p. 586) and 25 May 1901 (Proceedings p. 5) when dis- 

 cussing the culture conditions of the oligonitrophilous Cyanophyceae. 



In all these cases it is necessary as completely as possible to remove all soluble 

 organic substances from the solid medium, which is to be effected by a prolonged 

 washing with distilled water. The agar thus prepared, with the required nutrient 

 salts, for instance in the proportion: 



Distilled water TOO 



Agar 1.5 



K,HPO 4 o.oi 



KNOs (of NH4C1) o.oi 



is boiled and plated, and used for strew-or streakcultures originating from a film of 

 B. oligocarbophilus. Very soon the common saprophytic bacteria which never lack in 

 the film, are seen to develop on the plate and when these by their growth and respira- 

 tion have consumed the soluble carbon compounds, which were not yet removed from 

 the agar by the extraction with water, B. oligocarbophilus itself begins to grow. This 

 is usually the case after 14 days. Then, however, the colonies become easily recogni- 

 sable, our bacterium being the only species which in the given circumstances can feed 

 on the atmospheric carbon, and so go on growing, whilst the growth of all other 

 species soon comes to a stop. 



Even the colonies of the nitrifying ferments, which, as I have demonstrated before 

 (1. c.), can grow fairly well on this medium, when instead of nitrate an ammonium 

 salt is used, remain very small, never exceeding i mM. or less. On the other hand, 

 the colonies of B. oligocarbophilus attain dimensions of i cM. and more and may then 

 easily be transferred in a pure condition into test-tubes on the said medium. They 

 grow on the agar as thin, snow-white or rosy-tinted, very dry, flatly extended layers, 

 which strongly remind of the pellicle floating on the liquid. 



Nature, Vol.46, pag. 264, 1892. 



