A PARADOXICAL RELATION BETWEEN ZETA POTENTIAL AND SUSPENSION STABILITY IN S AND R VARIANTS OF INTESTINAL BACTERIA

The relation between electrokinetic potential and suspension stability of four strains of non-flagellate intestinal bacteria has been studied. The smooth forms have ζ-potentials which approximate zero over a wide range of pH and salt concentration, yet nevertheless form stable suspensions. The rough variants have ζ-potentials which vary with pH and electrolyte concentration in the familiar way. The rough forms have values of ζ-potential critical for their suspension stability.     

THE MODIFICATION OF ANTIBODIES BY FORMALDEHYDE

Certain strains of bacteria which have only minimal zeta potentials over a wide range of pH, and upon which surface deposits can be formed, afford a favorable means of studying certain chemical and physical properties of the surface deposits. Films of specific antibody-globulin upon these bacteria possess basic groups which can combine with formaldehyde. Combination of these groups with HCHO under the conditions of the present experiments shifts the isoelectric point of the sensitizing film toward the acid side by about 0.6 to 0.8 pH unit, and reduces the agglutinating tendency of the sensitizing film. Antibodies may be formalinized before combination with antigen without marked change in their specific combining affinities. The properties of the sensitizing films are similar whether formol treatment occurs before or after the antigen-antibody combination. The nature of the basic groups has been discussed.     

The role of human and mosquito behaviour in the efficacy of a house-based intervention

Housing improvement such as blocking eaves and screening windows can help in reducing exposure to indoor biting mosquitoes. The impacts of physical barriers could potentially be boosted by the addition of a mechanism that kills mosquitoes as they attempt to enter the house. One example is to combine household screening with EaveTubes, which are insecticide-treated tubes inserted into closed eaves that attract and kill host-searching mosquitoes. The epidemiological impact of screening + EaveTubes is being evaluated in a large cluster randomized trial in Cote d''Ivoire. The study presented here is designed as a complement to this trial to help better understand the functional roles of screening and EaveTubes. We began by evaluating householder behaviour and household condition in the study villages. This work revealed that doors (and to some extent windows) were left open for large parts of the evening and morning, and that even houses modified to make them more ‘mosquito proof’ often had possible entry points for mosquitoes. We next built two realistic experimental houses in a village to enable us to explore how these aspects of behaviour and household quality affected the impact of screening and EaveTubes. We found that screening could have a substantial impact on indoor mosquito densities, even with realistic household condition and behaviour. By contrast, EaveTubes had no significant impact on indoor mosquito density, either as a stand-alone intervention or in combination with screening. However, there was evidence that mosquitoes recruited to the EaveTubes, and the resulting mortality could create a community benefit. These complementary modes of action of screening and EaveTubes support the rationale of combining the technologies to create a ‘Lethal House Lure’.This article is part of the theme issue ‘Novel control strategies for mosquito-borne diseases’.