152 G. HAROLD DREW. 



In both cases a slight amount of Ammonia was recognizable by 

 Nessler's reagent when the nitrite reaction was strong, but decom- 

 position of the nitrite did not proceed further even after fourteen 

 days. 



At 32" C. cultures from tlie Marquesas showed trace of nitrite after 18 hours. 

 ,, ,, ,, gave strong nitrite reaction ,, 22 ,, 



„ „ 70 miles west of Ushant never gave 



nitrite or Ammonia reactions. 



The cultures from the Marquesas showed a slight amount of 

 Ammonia formation, but the decomposition of the nitrite did not 

 proceed further. 



From these experiments it appears that the bacteria from sub- 

 cultures from the Marquesas have a much greater denitrifying power 

 than those from subcultures from a point seventy miles west of 

 Ushant, and that as the bacteria from the Marquesas appear to be of 

 the same species as those investigated at the Dry Tortugas, their 

 power of causing complete denitrification in the modified Grran's 

 medium has been lost by cultivation on Peptone Agar, or during the 

 fourteen days journey from the Marquesas. 



The presence of the thick layers of fine chalky mud within the 

 Marquesas Keys, and elsewhere in many places near the Florida coast, 

 led to a consideration of the possibility of its precipitation by bacterial 

 agency. 



Since these bacteria grow freely in Gran's medium, the Calcium salt 

 of a simple organic acid is a sufficient source of organic food for them, 

 and it seems probable that they would thrive in sea-water containing 

 the products of decomposing vegetable matter, provided that the 

 nitrate supply and conditions of light and temperature were suitable. 

 Such conditions should be especially well fulfilled by the drainage 

 into the sea of a well-wooded country with a calcareous subsoil, and 

 the soluble organic Calcium salts carried to the sea in this way, would 

 there be precipitated as Calcium carbonate by the action of the bacteria. 

 In addition, the elimination of the acid radicle from the nitrate in the 

 process of denitrification, by whatever stages it may occur, must leave 

 the alkaline base free to destroy the normal equilibrium of the salts 

 in sea-water, and by increasing the alkalinity, would also result in 

 the precipitation of Calcium carbonate. 



To test this theory, cultures were made in a medium liaving the 

 following composition.: — 



Calcium succinate . . . . 2 "5 grammes. 



Potassium nitrate ..... 0"5 ,, 



Sea- water 1000-0 c c. 



