On the Relative Efficacy of the Doulton, Berkefeld and Brownlow Filters

In a previous communication (1906) it was shown by Bulloch and Craw that the Doulton “white filter” prevented the direct transimmission of micro-organisms, and that the filtrates from highly contaminated waters were germ free until sufficient time had been given for the bacteria to grow through the filter mass. It was demonstrated, in fact, that the Doulton filter was at least as efficient in the retention of micro-organisms as the best material on the market, viz. the Pasteur-Chamberland filter, and excelled the latter in its rate of filtration. It was pointed out that, with the possible exception of Kieselguhr, filters, only porcelain bougies could be relied upon to prevent direct transmission of germs. During the past year we have tested the relative efficiency of porcelain and Kieselguhr filters, in particular the Doulton porcelain filter and the Berkefeld Kieselguhr filter. A few samples of the Slack and Brownlow filter (sand and porcelain mixture?) were also tested.