ANAEROBIC CULTURES. 59 
crowded a tight-fitting, soft, rubber stopper. This end is finally buried for an inch 
or so in a small beaker of glycerin and is perfectly air-tight. A rimless test-tube 
about 5 inches (13 cm.) long and ofa diameter such that it will just slip easily up the 
other arm of the U-tube, is now packed by means of a pencil or glass rod with 8 or 
10 grams of pyrogallic acid, covered quickly with 25 cc. 
of 10 or 15 per cent caustic-potash water, and slipped up 
the open end of the tube, which is immediately plunged 
Sab into a dish of mercury and held there (under a shelf ) until 
enough of the oxygen is absorbed so that it will stay 
down of its own weight. ‘The exposure should be made 
at 25° or 30° C., or at least at temperatures considerably 
above zero, since the absorption of the oxygen is slow in 
cool air. 
The tube containing the pyrogallic acid and potash 
mixture floats on the mercury and rises, of course, in the 
arm of the U-tube as the oxygen is absorbed and the 
mercury enters it. ‘This tube must not, therefore, be too 
long so as to hit against the curves of the U-tube before 
all of the oxygen has been absorbed ; otherwise the mer- 
cury will pass up between the two tubes and overflow 
into the mixture. In other words, several centimeters 
must be allowed for the rise of the mercury. 
A few experiments will determine how much of the 
mixture is necessary for a tube of a given bore and how 
long it takes to absorb all of the oxygen.t ‘The level 
of the mercury in the open end with all the oxygen 
absorbed may be recorded by a scratch on the tube as a 
rough guide in subsequent work. At least half a dozen 
of these tubes will be found useful. ‘They may be made 
in any laboratory or may be procured from dealers in 
glassware. 
In the use of carbon dioxide, especially with sensitive organisms, two factors 
must be considered, (1) the simple exclusion of air, as in case of hydrogen, and 
(2) the change in the reaction of the medium due to absorption of the gas (forma- 
tion of carbonic acid). ; 
Fig. 55.* 
*Fic. 55—A simple device for growing organisms in air deprived of its oxygen. In the left 
arm are the cultures; in the right arm is a test-tube containing a mixture of pyrogallol and caustic- 
potash water. The beaker contains mercury. About one-third actual size. A modification of 
Ganong’s apparatus for study of germinating seeds, 
+ Macé states that 1 gram of the pyrogallol and 10 cc. of the 10 per cent potash-water are suffi- 
cient for each 100 cc. of air space. 
