DEPARTMENT OF MARINE BIOLOGY. I43 



On gelatin peptone (5 per cent peptone, kept at between 20° and 25° C. 

 to insure the medium remaining solid) growth was very slow. In stab 

 cultures growth proceeded slowly from the surface downwards, forming a 

 funnel-shaped depression of liquefied gelatin. Acid formation occurs in 

 glucose, mannite, and cane sugar, but not in lactose media. 



Growth is totally inhibited at a temperature of 10° C, but takes place 

 slowly at 15° C. 



Growth is much retarded by exposure to bright sunlight, but the bacteria 

 are not killed by a lo-hours exposure. 



The bacteria are facultative anaerobes, but growth under anaerobic con- 

 ditions is very slow. 



On Gran's medium growth is vigorous, and is accompanied by rapid de- 

 struction of the nitrate present. No growth occurs if the potassium nitrate 

 be omitted or if the calcium malate be replaced by calcium carbonate. 

 Growth in a pure solution of peptone in sea-water is slight, but becomes 

 abundant if potassium nitrate be added, when denitrification quickly ensues. 



A consideration of these results obtained in the Tongue of the Ocean 

 shows that the waters down to a depth of somewhere about 300 fathoms in 

 April 1 91 2 contains an enormously larger number of bacteria than the water 

 in the neighborhood of Tortugas in June 1911. The number of bacteria 

 falls off from about 14,000 to about 12 per i c. c. between depths of 250 

 and 350 fathoms; the temperature at 250 fathoms was about 15° C., and at 

 350 fathoms about 11° C., and it was shown in June 1911 at Tortugas that 

 B. calcis will grow slowly at 15° C., but that growth is totally inhibited at 

 10° C. It would thus seem that the observed distribution of the bacteria 

 agrees fairly with what might be expected from the temperature conditions. 



The much greater abundance of bacteria in the surface-waters of the 

 Tongue of the Ocean than in the waters around Tortugas may perhaps be 

 accounted for by the fact that in the former locality by far the greater part 

 of the surface-water must flow over the immense chalk mud-flats and shal- 

 lows which bound it in most directions, and, as will presently be shown, these 

 mud-flats are phenomenally rich in bacteria and are probably still being de- 

 posited by bacterial agency. 



BACTERIAL INVESTIGATION OE THE CHALKY MUD-ELATS TO THE 



WEST OE ANDROS. 



Samples of the mud were taken from the western entrance of South Bight 

 and from points 2 or 3 miles out from the shore, practically identical results 

 being obtained from all these localities. The sample at the mouth of the 

 bight was taken in about 4 feet of water, that 2 miles out in 7 feet, and that 

 3 miles out in 8 feet. The surface layer of the mud for a depth of about 

 6 inches was of a creamy white color ; below that it was of a grayish tinge 

 with a slight odor of sulphureted hydrogen. Microscopically the mud con- 

 sisted of minute unorganized particles, sometimes aggregated into larger 

 soft masses of irregular shape. The samples were necessarily taken from 

 the surface of the mud. 



For bacterial examination one part of this mud was shaken up with three 

 parts of sterilized sea- water. This was allowed to settle for 15 minutes, 

 and then the clearer surface layer was diluted i in 1,000,000 with sterilized 

 sea-water. The diluted fluid was plated in peptone agar, i c. c. being used 

 for each plate. The count of a number of plates after 48 hours gave 40 

 colonies as an average, and thus the mud itself must contain a minimum of 



10 — YB 



