Materials & Methods

    Three different commercial formulations of shampoos were refractometrically equilibrated for solute content. One contained cetrimide (cetavlon; Fig. 1), another contained polyquaternium-10 and the third formulation contained no "quats." Dosage was three drops per liter of contaminated water.

    Garden soil bacteria were most frequently used since they are generally benign for student use, and, more importantly, because they represent a very broad spectrum of types, within which are all the major bacterial pathogens. E. coli K1:O18ac:H7 was used as an analog for studying the effects of these treatments on other enterobacterial pathogens.

    Plate counts were used to assess the rates of killing of bacteria (nutrient and MacConkey agars), and for monitoring yeast removal (high-sucrose yeast agar). Motility was our index of viability of protozoans and other microscopic eukaryotes.

    Newspapers from cities around the world were collected, double-layered in baskets, and tested for their filtration ability (Fig. 2).

    While some assays were done using protozoans, most were done using bakers yeast, because both of availability and their being smaller than most protozoans.

    Tasting and consuming 250 mL of these dilute shampoo solutions was also carried out.