504 G, H, DREW. 



made in sterile sea-water, and a similar suspension containing roi^hly 

 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. 1 c.c. of each of these suspensions was then added to 

 1000 c.c. of the moditied Gran's medium : some of these cidtures were 

 kept at an average temperature 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. 

 „ „ ,, .. gave strong Nitrite reaction after 53 hours. 



„ ,, .,70 miles W. of Ushant showed trace of Xi trite 



after l-tO hours. 



„ „ .. 70 miles TT. of Ushant showed strong Nitrite 



reaction after 162 hours. 



In both cases a slight amount of Ammonia was recognizable by 

 Xesslers reagent when the Xitrite reaction was strong, but decomposi- 

 tion of the Nitrite did not proceed further, even after 14 davs. 



At 32' C. cultures from the Marquesas showed trace of Nitrite after 18 hours. 

 ,. ., ., .. gave strong Nitrite reaction after 22 



hours. 

 ,, ., j» ^0 miles W. of Ushant never gave Nitrite or 



Ammonia reaction. 



The culture from the Marquesas showed a slight amount of Ammonia 

 formation, but the decomposition of the Xitrite did not proceed 

 further. 



From these experiments it appears that the bacteria from sub- 

 cultures from the Man^uesas have a much greater deidtrifying power 

 than those from subcultures from a point 70 miles west of Ushant, 

 and that as the bacteria from the Marquesas appear to be of the same 

 species as those investigated at the Drv Tortugas, their power of 

 causing complete denitrification in Grans medium has t>een lost by 

 successive cultivations on Peptone Agar. 



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 mediimi, the Calciimi 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 



