Technique andApparatus forRapidand Inexpensive Enumeration ofBacteria

anda projection viewer were developed for use witha rapid bacterial counting technique employing agardroplets. The equipment allows theadvantages ofthetechnique tobeproperly realized and assists many conventional bacteriological tests which may bemadeatthesame time. Significant costandlabor savings are made,withreductions inincubation time, incubator space,andpreparative work. A rapid andinexpensive technique forenumerating bacteria, inwhichasample suspensionisdiluted inmolten agarandplated out instandard petri dishes asaseries of0.1-ml agardroplets, hasrecently beendescribed (3). Theunassisted manualmethoddiscussed in thefirst publication hasseveral advantages over conventional pour-plate counting methods in,forexample, quality control work infoodfactories, butitsattractions havebeen greatly increased bythedevelopment oftwo simpleaids.One,a foot-operated diluter/ dispenser, allows decimal orcentimal dilutions tobemadeandthedroplets tobeplated outrapidly witha minimumofeffort. The other, aprojection viewer, allows easyenumeration ofcolonies bythrowing abright imageof adroplet, magnified tothesize ofastandard petri dish, toward thetechnician ashesits at thebench. Thedroplet technique andthetwoaidsare inuseinanumberoflaboratories wherethe methodhasbeenmetwithremarkable enthusiasm. Thepresent paper describes thedevices anddiscusses theapplication ofthetechnique inquality control andresearch laboratories. MATERIALSAND METHODS Diluter/dispenser.