THE STUDY OF OBLIGATELY ANAEROBIC BACTERIA 123 



n lately 20 cm or 8 in. After this degree of evacuation is reached, con- 

 nect the rubber tube to the gas supply (a three-way stopcock facilitates 

 this change without loss of vacuum). Attach the electric plug (110- 

 volt alternating or direct current) and allow the gas and electric cur- 

 rent to remain attached for 30 to 45 min. At the end of this time 

 clamp the rubber tube tightly, remove the electric cord, and place 

 the jar in the incubator. (Formation of water droplets on the inside 

 walls of the jar indicates the proper functioning of the apparatus.) 

 To open the jar, remove the clamp. Insert a knife blade between lid and 

 rim of jar, using caution to avoid scoring the soft metal rim of the top and 

 making subsequent leakage more likely. If used with hydrogen, attach 

 the jar, without evacuation, to the hydrogen tank and admit the gas at a 

 pressure of 1-2 psi. Attach the electric connection, and allow the current 

 and gas both to remain on for 30 min. Then treat the jar as above. The 

 jar may be used as a gas-replacement system by evacuating the jar on a 

 water aspirator pump to 700 mm Hg negative pressure; fill with illumi- 

 nating gas, repeating this process three times or more. Avoid dropping of 

 agar from inverted plates due to excessive evacuation. This method may 

 fail to produce anaerobiosis as adequate as that achieved by catalytic 

 combustion as described above. 



Advantages. Convenient system for incubation of a number of plates in experi- 

 ments where speed of obtaining anaerobiosis is essential. Recommended for clinical 

 laboratories. Inexpensive system after the initial outlay for apparatus. Dis- 

 advantages. Some possibility of explosion or cracking of jar. Initial expense of 

 equipment is more than for other methods, but this may be a good investment if 

 routine work is to be done over a period of time. Requires source of hydrogen or 

 illuminating gas and electricity; while these are available in most laboratories, they 

 are not available in others such as some mobile laboratory units, temporary labora- 

 tories in field surveys, etc. 



Biological Methods for Oxygen Removal 



Vegetable-tissue Jar 



Materials for method of McClung, McCoy, and Fred (1935): (1) jar 

 or other container which may be^ sealed airtight (recommended: 6- by 

 18-in. or 6- by 12-in. Pyrex cylinder^) ; (2) square (7 by 7 in.) of plate glass 

 or a glazed plate; (3) plasticene,^ 3^ lb; (4) glass tumbler; (5) supply of 



1 Pyrex cylinder. Pyrex Catalogue No. 850. Corning Glass Works, New York, 

 or supply house. 



2 Sealing materials. Plasticene of a suitable grade is sold by Baltimore Biological 

 Laboratory, Baltimore, Maryland, and by J. L. Hammet Co., Cambridge, Massa- 

 chusetts. Care should be taken in choosing products for sealing, since some dry to 

 a hard cake upon incubation. A silicone grease is preferred by many workers, since 

 it gives a seal less likely to leak, and jar tops are more easily removed than with 

 plasticine. A suitable product is marketed as Dow-Corning High Vacuum Grease by 

 Do\y Corning Corp., Midland, Michigan. 



