— 164 — 
found on tlie bottom dose to shore, or apparently living in symbiosis with 
algae or plant on organisms. Thomsen [Wiss. Meeresunters , vol. XI, Kiel, 1910) 
has also found bacteria on the bottom of inshore waters which can convert 
nitrites into nitrates, and Drew suggested that similar bacteria having a nitri- 
fying action remain to be discovered in the open sea. 
5. The most interesting portions of the study are connected with the 
total number of bacteria noted in relation to depth, the observations being 
made otT the east coast of Andros Island, S. E. of Florida. In the first experi- 
ment, it was found after growth on cultures for AS hours, that the bacterial 
colonies varied as follows : 
DEPTH. N° OF COLONIES DEVELOPING FROM 1 CC. OF SAMPLE. 
Surface to loo fathoms Colonies uiicounlable owing to overcrowding, 
at 200 — i5oo and 17G0. Very much overcrowded. 
^00-600 — 1 /i to 1 7. 
822 — (bottom) 0 to 3. 
The second experiment was made at a point ih miles out to sea due east of 
Golding Cay (Andros Island). The results gave : 
N° OF BACTERIAL COLONIES 
DEPTH. DEVELOPING FROM 1 CC. OF SAMPLE. 
0-200 fathoms 1 3, loo- 16,200 
3oo — \U 
koo 19 
The third station was 1 0 miles E. N. E. 1/2 E. of Golding Gay. 
DEPTH. 
N OF BACTERIAL COLONIES 
DEVELOPING FROM 1 CC. OF SAMPLE. 
o-95o fathoms i3,3oo- i5,5oo 
35o — 16 
Thus it seemed obvious alike by experiment and by the theoretical considera- 
tions that bacteria do not exist below a given depth, in this case 200 to 200 
fathoms, and any denitrifying action due to them is brought to an end. 
With regard to the possibility of nitrogen-containing compounds being 
