58 BACTERIA IN RELATION TO PLANT DISEASES. 
precautions has led to the statement that certain strict aerobes are able to grow on 
ordinary media in the absence of oxygen, and that anaerobes are very uncertain in 
their behavior on standard media. Old pyrogallic acid should be avoided and some 
preliminary experiments should be made as to the rapidity of the absorption of the 
oxygen from a given space before the 
organism is tested. The writer found 
one brand of pyrogallol which re- 
moved the oxygen from a small space 
in six hours, another required about 
eighteen hours, a third required sev- 
eral days (time enough for a strictly 
aerobic organism to make a visible 
growth). Leaks may be detected read- 
ily by including with the cultures 
a fermentation-tube, the inclosed arm 
filled with water except for a small 
bubble of air. On absorption of the 
oxygen this bubble expands to a 
diameter which should remain con- 
stant if the jar continues air-tight. 
The gas remaining in receptacles 
from which the oxygen has been 
removed by the potash - pyrogallol 
method is not pure nitrogen, but 
nitrogen plus a variable small amount 
of carbon monoxide, which is said 
to be most abundant when the oxy- 
gen is absorbed slowly. ‘This small 
amount of CO is harmless to many 
bacteria, but the writer has some 
reason for suspecting that it is inju- 
rious to others, even if it does not entirely inhibit growth. 
The writer has found the following contrivance (fig. 55) a very simple one for 
testing the ability of organisms to grow in nitrogen : A U-tube of thick, clear glass, 
with arms about 10 to 12 inches long, open at the ends and having a uniform inside 
diameter of about 1 inch, serves as the culture-chamber and gas-receptacle. ‘T‘wo 
short, rimless, cotton-plugged test-tubes containing the media to be tested are inocu- 
lated and thrust one above the other into one arm of the U-tube, into which is then 
Fig. 54.* 
*Fic. 54.—Novy jar of Jarge size for Petri dishes and-numerous test-tube cultures. Clamped 
as when in use. Between the clamped parts is a rubber gasket, carefully waxed and vaselined. 
Darwin’s wax-mixture is advised. The writer also usually wires in the waxed top parts. The gas 
inflow is cut off by twisting the uppermost (horizontal) ground-glass stopper, which must be care- 
fully vaselined. One-third actual size, 
i 
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. 
