. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. ANAEROBIC CULTURES. 59 crowded a tight-fitting, soft, nibber stopper. This end is finally buried for an inch or so in a small beaker of gl)'cerin and is perfectly air-tight. A rimless test-tube about 5 inches (13 cm.) long and of a 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
. Bacteria in relation to plant diseases. Bacteriology; Plant diseases. ANAEROBIC CULTURES. 59 crowded a tight-fitting, soft, nibber stopper. This end is finally buried for an inch or so in a small beaker of gl)'cerin and is perfectly air-tight. A rimless test-tube about 5 inches (13 cm.) long and of a 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 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- cur}^ 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 mercur}^ 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 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 '^'s- ^^•* glassware. In the use of carbon dioxide, especially with sensitive organisms, two factors must be considered, (i) the simple exclusion of air, as in case of hydrogen,
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