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 oxygen. f 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, and 

 (2) the change in the reaction of the medium due to absorption of the gas (forma- 

 tion of carbonic acid). 



*FiG. 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. 



t Mace states that i gram of the pyrogallol and 10 cc. of the 10 per cent potash-water are suffi- 

 cient for each 100 cc. of air space. 



