regular further gas supply to be accompanied by positive removal of any accumulated condensate say preferably using a peristaltic pump which can also contribute to or assist in cabinet atmosphere removal at least after condensate removal is complete beneficial effect can be simply to increase tendency towards maintaining a prescribed or target atmosphere say as represented by flow rates of constituent gas further beneficial effect can be gained by taking account of such effects of particular microbiological action s of current interest as may be known or determined by further investigation in terms of differential effects on component gases say than by further prescribed modification of supplied gas mixture as further supplied say increasing flow rate s of one more and or reducing other s i e compared to normal target mix flows god according to type of such action s or further as to number s of samples involved yet closer internal atmosphere control can be obtained by sensing particular content s of one or more or all of constituent gases and computing individual gas flow rates to compensate whether wholly or partly specific implementations in practical embodiments of this invention will now be indicated and described by way of example with reference to the accompanying diagrammatic drawings in which fig1 is an outline atmospheric gas flow control provision for a first embodiment fig4 is an outline atmosphere control provision.