Endotoxins of Escherichia coli, Salmonella abortus equi and Serratia marcescens were examined using freeze-etch electronmicroscopy and light scattering techniques, with emphasis on their aggregation state. These endotoxins show distinct features of particle size and mass and they may be affected by the presence or absence of Ca2+ ions. No important differences were observed in the particle characteristics of the respective endotoxins in various infusion fluids.

Three asbestos‐free depth‐filters were compared with traditionally used asbestos‐containing depth‐filters for chemical integrity, physical integrity and pyrogen retention. With chemical and physical integrity only minor differences between the various filter types were seen. One asbestos‐free depth‐filter, based on charcoal, showed poor pyrogen‐retention; this might be due to a high flow rate used. Asbestos‐free depth‐filters based on kieselguhr or on a mixture of kaolin and alumina proved to be good alternatives; these filters have proved to be suitable for the removal of pyrogens from electrolyte‐ or carbohydrate‐containing infusion fluids.

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The electrokinetic properties of the endotoxins of Escherichia coli and Serratia marcescens have been examined. Both endotoxins are negatively charged, with the zetapotential being increased by the presence of cations whose relative influence resembles the Schulze-Hardy rule for colloid stability. Fe3+ and Th4+ ions are capable of reversing the negative charge of the endotoxin particles to positive. These cations were found to have a strong inhibitory effect on the activity of endotoxins in the limulus amoebocyte lysate test but the inhibitory effect did not parallel changes in the zetapotential because the effect occurred at concentrations too low to affect this parameter.

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