THE PRECIPITATION OF CALCIUM CARBONATE IN THE SEA. 503 



reaction was obtained, and a slight Ammonia reaction was given 

 with Nessler's reagent. The process of denitrification, even after 

 the lapse of weeks, did not extend beyond this, and no bubbles of gas 

 were formed. Other experiments made with subcultures from Agar 

 and Gelatin media gave similar results, so that it appears that this 

 bacterium cannot entirely break down Xitrates at a temperature of 

 20° C. The optimum temperature for denitrification produced by this 

 bacterium appears to be about 20° C, as the process was less rapid at 

 average temperatures of 17° C. and 25' C. At a temperature of 32' C. 

 rapid growth 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 it is possible 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 Ba.cteriv.m 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 OF WATER FEOM THE 

 MARQUESAS KEYS AND THE EXPERIMENTAL PRE- 

 CIPITATION 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 within the atoll were sent to me at Plymouth by post, and ex- 

 amined fourteen days after collection. 



On plating on Peptone Agar, an average of 800 colonies per 1 c.c. of 

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

 species, and in appearance and all cultural characteristics were identical 

 with the Bacterium calcis previously described as occurring around the 

 Tortugas. 



A suspension of these bacteria from a culture on Peptone Agar was 



