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BIOLOGY OF BACTERIA.                    55

employed. They are filled with glucose bouillon, steril-
ized as usual, inoculated and allowed to grow. If gases
are formed, the bubbles ascend and the
gas accumulates at the top of the tube.
In estimating quantitatively, one must
be careful that the tube is not so con-
structed as to allow the gas to escape as
well as to ascend in the main reservoir.
For the determination of the nature
of the gases ordinarily produced, sonic
of which are inflammable and some not, f.         ......

.    ,        '      H<;. 5.—Smiths fcr-

Theobald Smith has recommended the       mentation-tube.
following methods:

"The bulb is completely filled with a 2 per cent, so-
lution of sodium hydroxid (NaOII) and tightly closed
with the thumb. The fluid is shaken thoroughly with
the gas and allowed to flow back and forth from the bulb
to closed branch, and the reverse several times to insure
intimate contact of the COa with the alkali. Lastly,
before removing the thumb all the gas is allowed to col-
lect in the closed branch so that none may escape when
the thumb is removed. If CCX be present, a partial
vacuum in the closed branch causes the fluid to rise sud-
denly when the thumb is removed. After allowing the
layer of foam to subside somewhat the space occupied by
gas is again measured, and the difference between this
amount and that measured before shaking with the
sodium hydroxid solution gives the proportion of C()$
absorbed. The explosive character of the residue is
determined as follows: uThe cotton plug is replaced and
the gas from the closed branch is allowed to flow into the
bulb and mix with the air there present. The plug is
then removed and a lighted match inserted into the
mouth of the bulb. The intensity of the explosion varies
with the amount of air present in the bulb."

7, Production of Odors.—Of course, such gases as H2S
and NBu are sufficiently characteristic to be described as
odors. There are, however, a considerable number of