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SummaryA number of improvements have been made in a totally-automated antibiotic bioassay machine previously described. The new machine accepts unmeasured, untreated, opaque suspensions of fermentation beers three times faster (120 samples per hour) and supplies printed potencies sooner (in just over two hours). Whereas the original machine employed a self-cleaning filter and used disposable two milliliter beakers, this version involves a batch-dialysis scheme for effecting sample purification, and provides for automated cleaning of incubation chambers.In operation, a measured portion of thoroughly-mixed fermentation beer is automatically diluted and transferred into one side of an incubation chamber, the two halves of which are separated by a dialysis membrane. The other half i6 filled with inoculated media. During the two hour incubation at 37", dialyzable antibiotic limits growth of the inoculum in proportion to its concentration. After incubation, the turbidity of the inoculum is simultaneously read by an online computer and plotted on a strip chart recorder. The computer supplies printed potency values and sample identification on site, while the recording provides the operator with an analog record of turbidity. Fiber optics are employed in the turbidimetric readout., and an electric typewriter provides the printout.