Experiments with Bacterial Filters and Filterable Viruses

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Abstract
The ability of bacteria, dyes, or other colloids to pass through filters depends not solely upon the size of the filter pores but also upon the electrical charge of the filter. Thus the basic dye, Victoria blue, which did not pass through the negatively charged siliceous, (Berkfeld) filter, readily passed through an oppositely charged filter of plaster of Paris; while the reverse was true of the acid dye, Congo red. By the use of a filter so made that the core of Berkfeld composition had a cortex of gypsum, dyestuffs, viruses, and colloids bearing either a positive or negative charge could be removed by filtration. The following so-called filterable viruses failed to pass the gypsum filter: the bacteriophage of Staphylococcus aureus, Vibrio percolans, the mosaic of tobacco, vaccine virus, and the virus of rabies. By filtration through the gypsum filter with 25% MgO2 diphtheria toxin, botulinus toxin, abrin, and tuberculin were removed. As a rule all narcotizing toxins and drugs are filtered out with the basic filter, and spasm-producing toxins and drugs with the acid filter; which makes it probable that the respective nerve cells attacked by these 2 classes of agents have a similar though opposite difference in reaction or charge.

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