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Biomedical subjects

G W PEARCE

Publications and source records attributed to G W PEARCE.

At least 19 recordsLinked to original sources
PubMed1963

DICHLORVOS AS A RESIDUAL FUMIGANT IN MUD, PLYWOOD AND BAMBOO HUTS.

In experiments conducted at Savannah, Ga., dichlorvos dispensers of montan (lignite) wax installed at a rate of six units per 1000 cubic feet (28 m(3)) in huts with mud or bamboo walls and with thatched roofs produced kills of caged Anopheles quadrimaculatus (12 hours' exposure) at or above 95% for 5-6 weeks. The doors, windows, and eaves of the huts were open for maximum ventilation. In a non-ventilated plywood hut, a single dispenser gave effective kills for 7 months but in a non-ventilated mud hut the period was 5 months. Air concentrations of dichlorvos in the mud hut were shown to be definitely lower than those in a plywood hut at the same dosage level.

Animals↗
PubMed1961

Insecticidal vapours for aircraft disinsection.

A general discussion of the problem of aircraft disinsection is presented. The weaknesses of the present aerosol method, the limitations imposed by airline operators, government officials, passengers, and others, and the potential value of insecticidal vapours as a means of aircraft disinsection are discussed. An apparatus is described for screening insecticides for their vapour toxicity to houseflies and mosquitos. This apparatus led to the discovery of DDVP (O,O-dimethyl-2,2-dichlorovinyl phosphate) and its remarkable vapour toxicity to insects, and to the subsequent studies of its potential use in the vapour state for aircraft disinsection.

Aerosols↗
PubMed1961

A mechanical system for dispensing known amounts of insecticidal vapours.

The requirements for a self-contained semi-automatic insecticidal vapour dispenser for use in the disinsection of aircraft are presented. A prototype device meeting these requirements is described and data on its performance, using DDVP (O,O-dimethyl-2,2-dichlorovinyl phosphate) as the insecticide, are given. In this system a miniature air compressor forces air through a membrane impregnated with DDVP, and the vapour-laden air exits into the cabin through a tubular distribution system equipped with orifices. The vapour output is governed by the volume and the temperature of the air passing through the membrane, and the system is adaptable to all types of aircraft at present in use or projected for the near future. The system can also be adapted for use in the disinsection of other closed or semi-closed spaces.

Aerosols↗
PubMed1959

Factors affecting the suspensibility of DDT water-dispersible powders.

The authors describe some experiments carried out to determine the effect of moisture, temperature, and pressure on the suspensibility of DDT water-dispersible powders.It was found that the removal of moisture brought about a slight increase in suspensibility; that heating for one hour at temperatures below 70 degrees C resulted in an increase in suspensibility, due probably to the drying effect of the heat, whereas heating for the same period at temperatures above 70 degrees C resulted in a decrease; that on prolonged heating at 70 degrees C and 75 degrees C the suspensibility decreased sharply in the first four hours but thereafter showed little change up to 20 hours; and, finally, that low pressures-for example, 25 g per cm(2)-had little effect on the suspensibility, but that at pressures of 100 pounds per square inch (7 atm.) and over, it varied in inverse proportion to the logarithm of the pressure.

DDT↗
PubMed1959

Storage stability of DDT water-dispersible powders.

The authors describe a study of the change in suspensibility of two series of 75% DDT water-dispersible powders during storage in simulated commercial packages at 27 degrees C, 50 degrees C and 65 degrees C and as "shelf" samples at ambient temperatures. All the products tested in both series were made under the conditions of regular commercial production, and all those in the second series were prepared in 1954 under contract to the International Cooperation Administration (ICA) and according to ICA specifications.THE RESULTS SHOWED THAT: (a) a high initial suspensibility is no criterion of "shelf" life; (b) the suspensibility after the so-called "tropical storage pre-treatment" is no criterion of stability, except perhaps in the case of very poorly formulated products; (c) periodic observations, made over a period of a month or more, of the suspensibility of powders stored in commercial or simulated commercial packages at 50 degrees C and 65 degrees C will provide an indication as to the probable long-term stability of the products in question; and (d) it seems likely that a reasonable estimate of long-term storage stability at ambient temperatures could be obtained by subjecting the samples to high temperatures for a very short period.

DDT↗
PubMed1959

Specifications of the International Cooperation Administration for DDT water-dispersible powder for use in malaria control programmes.

Background information is presented on the development of specifications for 75% DDT water-dispersible powder for use in malaria control programmes supported by the International Cooperation Administration (ICA) of the United States Government. Early difficulties with DDT powders used in these programmes were investigated and it was found that the most critical requirements involved packaging, suspensibility and storage stability. ICA specifications were evolved to meet these requirements. The suspensibility test developed is described, and the importance of inspection of the material procured is discussed.

DDT↗
PubMed1959

Factors affecting the suspensibility of dieldrin water-dispersible powders.

Various dieldrin water-dispersible powder formulations have been subjected to elevated temperature storage and the effect on their suspensibilities compared. The Shell Chemical Company's 50% dieldrin formulation AC 1630 was recommended for use in the malaria control programmes of the International Cooperation Administration rather than its 50% formulation AC 1631, on the basis of superior performance after storage at 50 degrees C and 65 degrees C. In a similar series of tests on 75% dieldrin water-dispersible powders, Shell formulation AC 1621, which contains Hi-Sil as diluent, was judged better than AC 6621, which contains Micro-Cel as diluent. A series of samples of AC 1621 was subjected to temperatures of 90-120 degrees C for periods of 1-20 hours and the effect on suspensibility determined. Most samples withstood the treatment reasonably well at temperatures up to 110 degrees C for 20 hours.

Dieldrin↗