On the Precipitation of Calcium Carbonate. 29 



rapid at average temperatures of 17° C. and 25° C. At a temperature of 

 2,2° C, rapid growtli took place, but no denitrification resulted. 



It should be noted that these temperature observations were only made 

 with subcultures from colonies on peptone agar and peptone gelatin media, 

 and there is reason to believe that the power of denitrification becomes 

 diminished after cultivation on such media. Further and more accurate 

 temperature experiments are required in which the culture medium is 

 directly inoculated with freshly collected samples of water. 



This bacterium appears to be closely related to the Bacterium calcis, 

 its chief points of difference being : 



1. Lesser denitrifying power and lower temperature optimum for denitri- 



fication. 



2. More rapid growth on gelatin media. 



3. Absence of acid formation in media containing cane sugar. 



INVESTIGATION OF SAMPLES FROM MARQUESAS KEYS. AND EXPERIMENTAL 

 PRECIPITATION OF CALCIUM CARBONATE BY BACTERIAL AGENCY. 



The Marquesas Keys constitute a coral atoll which forms part of the 

 long chain of keys separating the Gulf of Mexico from the Straits of Florida. 

 Within the atoll the water is very shallow and the bottom consists of a 

 fine chalky mud many feet deep. Samples of the water from the lagoon 

 of the atoll were sent to me at Plymouth by post, and examined 14 days 

 after collection. 



On plating on peptone agar, an average of 800 colonies per I c.c. of the 

 sample were obtained. These colonies appeared to be all of one species, 

 and were identical in appearance and in all cultural characteristics with the 

 Bacterium calcis previously described as occurring around the Tortugas. 



A suspension of these bacteria from a culture on peptone agar was made 

 in sterile sea-water, and a similar suspension containing roughly the same 

 number of bacteria was made from a third subculture on peptone agar of 

 the bacteria obtained from the station 70 miles west of Ushant. i c.c. of 

 each of these suspensions was then added to 1,000 c.c. of the modified 

 Gran's medium. Some of these cultures were kept at an average tem- 

 perature of 20° C. and others at 32° C., with the following results: 



At 20° C. cultures from Marquesas showed trace of nitrite after 45 hours. 



At 20° C. cultures from Marquesas gave strong nitrite reaction after 53 hours. 



At 20° C. cultures from 70 miles west of Ushant showed trace of nitrite after 140 hours. 



At 20° C. cultures from 70 miles west of Ushant showed strong nitrite reaction after 162 



hours. 

 In both cases a slight amount of ammonia was recognizable by Nessler's reagent 



when the nitrite reaction was strong, but decomposition of the nitrite did 



not proceed further even after 14 days. 

 At 32° C. cultures from the Marquesas showed trace of nitrite after 18 hours. 

 At 32° C. cultures from the Marquesas gave strong nitrite reaction after 22 hours. 

 At 32° C. cultures from 70 miles west of Ushant never gave nitrite or ammonia reaction. 

 The cultures from the Marquesas showed a slight amount of ammonia formation, 



but the decomposition of the nitrite did not proceed further. 



