Automatic control for evacuating anaerobic jars.

Displacement of oxygen by an inert gas is a method for attaining anaerobiosis which is preferred by many bacteriology laboratories because of the low cost of the process, and because of the small but real danger of explosion when the alternative, hydrogen with ignition, is used. Several cycles of evacuation and filling are necessary; usually, oxygen-free nitrogen is used with a final charge of a nitrogen-carbon dioxide mixture. Such a system has been used for many years in the diagnostic laboratory of the Boston City Hospital with excellent results, including the growth of fastidious organisms such as Bacteroides. As currently practiced, however, the procedure is timeconsuming and tedious, and there is a danger of by Schaedler et aL Evacuation begins as the control is turned on. Adjustable mercury pressure switches alternately operate a vacuum pump and regulate 'as flow through solenoid valves attached to standard gas regulators (Fig. 2 ). One of six neon lighits indicates the filling cycle. If the filling processon a previous run has been prematurely interrupted, the proper starting cycle may be obtained by flicking the mode selector on and off during the filling phase of the cycle. Overfilling in cases of control failure is prevented by a lowpressure safety valve. A "Manual" mode and separate switches permit independent operation of tank valves and vacuum pump. Components for construction of the control are readily available from commercial sources. Total