500 G. H. DKEW. 



slum malate and 0*5%^ Potassium nitrate in sea-water, but in this 

 medium growth apparently ceased after a few days and denitrification 

 was never complete ; a slight precipitation occurred, and the solution 

 was found to have very definitely increased in alkalinity. 



This bacterium does not appear to have been previously described, and 

 I propose for it the name of " Bacterium calcis," owing to its power of 

 precipitating Calcium carbonate from solutions of Calcium salts. This 

 point will be dealt with later in the paper. 



The characteristics of the scarcer non-denitrifying form of bacterium 

 found on the Agar plates are as follows : — 



The morphological characters are exactly similar to those of B. calcis. 



Growth on the Potassium malate Agar medium is very slow and in- 

 definite. On Peptone Agar growth is somewhat slower than in the 

 case of the B. calcis. On the surface, circular cream-coloured 

 colonies are formed, having a brownish centre, the edges are smooth and 

 regular, and the colony remains discrete and does not tend to spread. 

 The deep colonies are smaller and usually ovoid in shape, and of a 

 somewliat darker colour than those on the surface. 



No growth was obtained on Gelatin media. 



Acid formation, as shown by the Neutral Pied reaction, occurs in 

 Dextrose and Laevulose, but not in Cane Sugar, Lactose, or Mannite 

 media. 



Growth takes place slowly at 10° C. No visible growth occurred at 

 0" C, but cultures were not killed by twenty-four hours' exposure 

 to this temperature. 



Growth is retarded by light, and cultures are killed by four hours' 

 exposure to bright sunlight. 



The bacterium is a strict aerobe. 



Free growth takes place in Gran's medium, but develops much slower 

 than in the case of the denitrifying form : no growth occurs if the 

 Potassium nitrate be omitted entirely, but takes place freely if a mere 

 trace in excess of that normally present in the sea-water be added, 

 though no denitrification results. Attempts were made to discover 

 whether this bacterium had any nitrifying or denitrifying action in 

 various culture media, but uniformly negative results were obtained. 

 Nitrites were neither oxidized to Nitrates, nor reduced to Ammonia or 

 free Nitrogen, and Ammonia salts were unaffected. No growth was 

 obtained in any culture medium that did not contain at least a trace of 

 Nitrates, so it was not practicable to ascertain whether the bacterium 

 had a nitrifying action without the necessary facilities for quantitative 

 work. 



On one occasion samples were obtained from various depths up to 



