140 



REPORTS ON INVESTIGATIONS AND PROJECTS. 



ammonia or free nitrogen, and ammonium salts were unaffected. No growth 

 was obtained in any culture medium that did not contain at least a trace of 

 nitrates, so it was not practicable to ascertain whether the bacterium had a 

 nitrifying action with the apparatus available. 



On one occasion samples were obtained from various depths down to 90 

 fathoms at a point in the Gulf Stream 25 miles south of Tortugas. For this 

 purpose glass flasks of about 300 c.c. capacity with narrow recurved drawn- 

 out necks were exhausted and sealed ; they were then lowered in an appa- 

 ratus by which the extremity of the neck could be broken off at any desired 

 depth by sending a messenger down the sounding wire, when the flasks 

 became completely filled with water. These samples were plated and counted 

 with the average results shown in the table. 



If any deductions can be made from one series of observations, it would 

 seem probable that the non-denitrifying bacteria are a deep-water form, and 

 this would be upheld by the ease with which they are killed by exposure to 

 sunlight. On the other hand, the denitrifying bacteria would appear to be a 

 surface form reaching their maximum a little below the surface. This would 

 be upheld by the results obtained in Jamaica, in which it was shown that 

 denitrification occurred much more rapidly in cultures made from samples 

 collected from depths of 3 and 6 fathoms, and possibly explained by the fact 

 that the growth of the bacteria is inhibited by strong light. 



On August 7, 1911, two samples of water were collected in the lagoon of 

 the Marquesas Islands, 40 miles east of the Tortugas. These samples were 

 obtained near the eastern entrance to the lagoon, while the tide was still 

 ebbing but nearly low. The bottles were sent to Plymouth, England, where 

 they were studied with the following result : 



Sample of Water from Marquesas Keys. 



The salinity of the lagoon water was low, being only 33.95. 



Plated on peptone agar, i c.c. = 800 colonies (average of 5 plates). Colonies appear 

 all of same kind. 



Agar. — After 24 hours (at 75° F.) colonies are white, circular, with finely irregular 

 outline. Superficial colonies are considerably elevated, slightly granular, and spread 

 rapidly. Deep colonies remain small and circular. Old cultures become yellowish and 

 the color may spread through the agar. 



Gelatin stabs. — Growth mostly superficial, with liquefaction; very slight growth in 

 deeper parts of stab. 



Glucose, peptone, neutral red medium = acid formation. 



Cane sugar, peptone, neutral red medium = acid formation. 



Mannite, peptone, neutral red medium = acid formation. 



Lactose, peptone, neutral red medium = no acid formation. 



Rapid growth and denitrification in the modified Gran's medium. 



Rapid growth in a medium consisting of calcium succinate i.o gram (soluble), potas- 

 sium nitrate 0.5 gram, and sea-water 1,000.0 c.c, with production of thick, milky 

 appearance, due to extremely finely divided particles of calcium carbonate, so fine that 

 they will not settle. 



