NOTES ON ANTARCTIC BACTERIOLOGY. 145 



Weddell Sea ; but, judging by the results obtained in cultures kept at temperatures 

 approximating to those constantly prevailing in that sea, and even in those kept at 

 temperatures considerably higher, it seems at least doubtful if much active, denitrification 

 can be carried on by bacteria in those waters. The question of deuitrification being- 

 carried on by organisms other than bacteria, such as Euglena, seems possible from three 

 or four observations (see Nos. 11, 12, and 14 quoted above). 



Brandt in particular has pointed out the important role played by denitrifying 

 organisms in marine metabolism, setting free again the great mass of nitrogen which is 

 brought into the ocean in the form of nitrate, nitrite, and ammonia salts, and breaking 

 down dead organic matter. He has propounded the view, based on the fact that polar 

 seas are very rich in plankton, while tropical seas are comparatively poor, that the activity 

 of denitrifying organisms is far greater in warm seas than in cold, while nitrification, 

 on the other hand, is probably more active in polar seas. In other words, in polar seas, 

 owing to the low temperatures, the denitrifiers cannot break down nitrogen-containing 

 matter to the same extent, so that a richer plant life, and, in consequence, a richer animal 

 life, can exist in them than in warm seas where the nitrogenous matter is broken down, 

 often to the extent of liberating free nitrogen. 



These investigations certainly tend to support Brandt's views to a considerable 

 extent. The presence of active nitrification could not be substantiated, as is mentioned 

 further on, nor is it from the observations of Dr Gazert, who also failed to obtain any 

 evidence of marine nitrifying organisms. The presence of denitrifying organisms, on 

 the other hand, seems to be widespread in the Weddell Sea, but their activity under 

 the low temperature conditions prevailing seems to be very slight. 



Gazert records fairl) 7 similar conditions. Using Bauer's media, which I did not 

 employ, he found denitrifying organisms to be present in the cold Antarctic waters, 

 though apparently in very small numbers. With regard to their activity, he found that 

 at temperatures from 5 C. to 10 C. (40 F. to 50 F.) denitrification proceeded very, very 

 slowly, but fairly actively between 20 C. and 25 C. (68 F. to 77 F.). Using Gran's 

 media, however, he does not appear to have obtained denitrifying organisms. 



(c) Quantitative Estimations of the Bacterial Content of Sea Water. 



1. Surface water, 13th Feb. 1903, lat. 59 43' S., long. 30 44' W. Medium G 



(see under notes on "Denitrifying Organisms"), 1 c.c. of water melted in with 

 the medium in a Petri dish. Incubated in laboratory, temperature 35 F. 

 to 55 F. 



Result, 170 colonies. 



2. Same as No. 1, only incubated at 60 F. 



Result, 334 colonies. 



3. Surface water, 24th Feb. 1903, lat. 69 52' S., long. 17 22' W. Medium G. 



1 c.c. of water. Incubated first in laboratory ; later at 60 F. 



Result, 35 colonies. 

 VOL. III. 19 



