On the Precipitation of Calcium Carbonate. 



27 



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 un- 

 affected. 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 facili- 

 ties for quantitative work. 



On one occasion samples were obtained from various depths up to 90 

 fathoms at a point near the Gulf Stream region, 25 miles south of Tortugas. 

 Exhausted glass flasks with capillary necks which could be broken off at 

 the required depth were used for the purpose. 



These samples were plated in the peptone agar medium and counted, 

 with the following average results: 



These figures are probably not very reliable, especially for the greater 

 depths, since it is possible that many of the bacteria were killed by the sud- 

 den reduction of pressure to which they were exposed as the water entered 

 the exhausted bulb. 



INVESTIGATION OF SAMPLES FROM A POINT 70 MILES WEST OF 

 USHANT ISLAND, FRANCE. 



This spot was chosen as it is sufficiently far out in the Atlantic to be 

 largely removed from the influence of the English Channel water. The 

 object was to investigate truly oceanic bacteria, and previous work in 1909 

 had shown that the bacterial flora of the Channel water was relatively very 

 complicated, probably owing to the presence of littoral forms. The Marine 

 Biological Association of the United Kingdom very kindly sent their 

 steamship Oithona from Plymouth for this work, and gave me every facility 

 both on board and in their laboratory. As in Tortugas, the deep samples 

 were collected in exhausted glass flasks, and accordingly, as previously ex- 

 plained, the results obtained from the deep samples can not be considered 

 to possess any very great degree of accuracy. 



Attempts were made to plate the sample in peptone agar on board the 

 boat, but the result was not satisfactory, as owing to the motion of the boat 



