THE PRECIPITATION OF CALCIU.M CARBONATE IN THE SEA. 495 



accumulation of the products of metabolism had become toxic to the 

 bacteria. 



It was found tliat the rate of denitrification varied with the 

 temperature, and that in cultures kept at a temperature of between 

 10° and 12° C. no growth or denitrification occurred. The denitrifica- 

 tion Avas always more rapid in cultures from water taken from a depth 

 of o or 6 fathoms than from the surface. It was also more rapid with 

 samples taken from the thick muddy water of a mangrove swamp, 

 where organic matter was plentiful. 



The bacteria present in the cultures were very minute, actively 

 motile bacilli with rounded ends. 



An abstract of the behaviour of a few of the cultures is given 

 below. 



1. Sample collected 5 miles S. of Port lloyal, wind S.E., force 4, tide 

 rising. Sample taken from surface. 1000 c.c. of Gran's medium was 

 inoculated with 10 c.c. of sample. 



After '20 hours a slight cloud developed in the culture, and faint Nitrite 



reaction was given. 

 After 36 hours a dense cloud developed in the culture, and strong Nitrite 



reaction was given. 

 After 60 hours a dense cloud and scum developed in the culture, and strong 



Nitrite and faint Ammonia reaction was given. 

 After 70 hours a dense cloud, scum, and bubbles developed in the culture, and 



faint Nitrite and faint Ammonia reaction was given. 

 After 84 hours culture was less cloudy, with much scum, no Nitrite or Nitrate 



reaction, very faint Ammonia. 

 The average temperature at -which the culture was grown was 30° C. 



2. Sample collected from same spot under similar conditions, from a 

 depth of 3 fathoms. 1000 c.c. Gran's medium was inoculated with 

 10 c.c. of sample. 



After 20 hours a slight cloud developed in the culture and faint Nitrite 



reaction was given. 

 After 27 hours a denser cloud developed in the culture and strong Nitrite and 



faint Ammonia reaction was given. 

 After 38 hours a dense cloud and scum developed in the culture and strong 



Nitrite and faint Ammonia reaction was given. 

 After 48 hours a dense cloud and scum developed in the culture and moderate 



Nitrite and faint Ammonia reaction was given. 

 After 63 hours a moderate cloud, thick scum, and bubbles developed in the 



culture and faint Ammonia reaction was given. 



NEW SERIES. — VOL. IX. NO. 4. MARCH, 1913. 2 K 



