188 OUTLINES OF BACTERIOLOGY 



slight turbidity just above the sediment of the culture fluid, or at 

 the same place, a strong opalescence. A microscopical examination 

 reveals not only Zoogloea masses but also free-swimming individuals 

 and all stages of intermediate conditions. If examined a day or two 

 later, when all the ammonia of the culture fluid will have been used 

 up, it will be found that the motility has been lost, and all the 

 individuals will have sunk into the sediment at the bottom of the 



culture fluid. Fig. 114 shows the micro- 

 ^J scopic appearance presented by the free- 



f swimming individuals. The form of the 



mL individuals, as seen in the figure, is like 



f the letter 0, the width being 0-9-1 -0 /A 

 and the length 1-2-1 -8^. 



Motility is effected by the activity of 

 one somewhat elongated cilium attached 



FIG. 114. Nitrite-bacteria. (Zurich.) 



Free-swimming individuals. to one ot the ends. Ihe greater the 



predominance of the free motile indi- 

 viduals over those embedded in the Zoogloeae the greater is the 

 capacity for oxidation possessed by the culture, and, it follows, the 

 quicker is the rate of transformation of the ammonia-compound into 

 the nitrite. When the ordinary nutrient media, bouillon, nutrient 

 agar, nutrient gelatine, etc., are inoculated with these bacteria, no 

 trace of growth is observed. As will be presently seen, these 

 organisms derive their nitrogen from the ammonia compound, and 

 their carbon from the carbon dioxide of- the atmosphere. 



With regard to the nutrient solutions for the cultivation of these 

 bacteria, the best results have been got from the following : 



(1) or ^ (2) 



Ammonium sulphate, - 1 gram Ammonium sulphate, 1 gram 



Potassium phosphate, - 1 ,, Potassium phosphate, 1 ., 



Well-water, - - 1 litre Magnesium sulphate,- 0-5 



Basic magnesium sulphate in Sodium chloride, - 2 grams 



excess. Ferrous oxide, - - 0-4 gram 



Distilled water,- - 1 litre 

 Basic magnesium sulphate in excess. 



or (3) 



Ammonium sulphate, 2-2 -5 grams 



Potassium phosphate, 1 gram 



Magnesium sulphate, 0-5 



Calcium chloride, - trace 



Distilled water, 1 litre 



Basic magnesium sulphate in excess. 



(About 1 grain of basic magnesium sulphate per -J^ gram of 

 ammonium sulphate has been recommended.) 



