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Biomedical subjects

R S Thomas

Publications and source records attributed to R S Thomas.

At least 55 records · Page 3Linked to original sources
PubMed1981

Localization of DNA phosphorus in Tipula iridescent virus by oxygen plasma microincineration. I. Electron microscopy of ash structures.

Tipula iridescent virus (TIV) is a relatively large particle containing about 15% DNA. As shown elsewhere by X-ray microanalysis (Thomas RS, Corlett M: J Histochem Cytochem 29:394, 1981), low-temperature oxygen plasma microincineration of the virus produces a stable phosphorus oxide ash representing this DNA nearly quantitatively. Transmission electron microscopy (TEM) of entire particles after plasma incineration shows the ash confined to the viral cores, confirming the previously known general location of the nucleic acid. Examination of ultrathin-sectioned virus crystals after plasma etching or ashing shows, on a still finer scale, that the DNA is probably confined to a shell structure within the core. A fine trace of ash from the capsid, seen in some preparations, may represent a phospholipid internal membrane known to be present. The possibilities of ash pattern artifacts are discussed. Heating experiments show that the ash patterns (and native virus particles) evaporate completely at high temperature, consistent with their presumed polyphosphoric acid composition. A heat-stable ash could be formed, however, when the viral DNA became accidentally stained with iron from the steel TEM grids used--a noteworthy artifact. The present work suggests some future possibilities of the plasma microincineration technique. In particular, the ability to see directly the fine distribution of mineral concentrations in ash patterns with the full resolution of TEM should be a powerful adjunct to increase effectively the sensitivity and resolution of X-ray microanalysis of mineral constituents in biological specimens.

DNA, Viral↗
PubMed1981

Localization of DNA phosphorus in Tipula iridescent virus by oxygen plasma microincineration. II. Electron probe X-ray microanalysis of ash constituents.

Microincinerated, 1-micrometer sections of Tipula iridescent virus (TIV) crystals were analyzed quantitatively with a wave-length-dispersive electron microprobe to determine the chemical composition of high-resolution ash patterns previously obtained from ultrathin sections of the same specimen (Thomas RS: J Histochem Cytochem 29:379, 1981). Parallel analyses were performed on intact sections. In some cases, the same section and probe tracks were analyzed both before and after ashing. The principal elemental constituent of the ash was phosphorus, representing nearly all of the phosphorus found in the unashed sections. This confirmed the likely DNA origin of most of the ash. Other elements--sulfur, calcium, sodium, and perhaps carbon and nitrogen--found in relatively small concentrations in the ash, were partly due to either to incomplete ashing or to a particulate contaminant. Similar plasma ashing and analyses of sectioned model preparations of polymethacrylate containing dissolved triphenyl phosphate confirmed that phosphorus, by itself, could be retained as a stable ash. Analyses of polymethacrylate containing aluminum as well as phosphorus disclosed an unexpected artifact--aluminum inhibited the plasma ashing. These results suggested that the wavelength-dispersive probe, able to analyze for carbon and nitrogen as well as mineral elements, should be a generally useful tool in analyzing plasma microincineration phenomena, where macroscopic results do not apply. Relatively high beam intensity used throughout the probe analyses caused obvious damage to intact sections, particularly when they were mounted on thin-film supports. In contrast, the ash appeared quite stable. This suggested that plasma ashing of biological sections, converting them into mineralogical specimens, may be generally useful in probe analyses of mineral constituents, permitting greater sensitivity via higher beam currents, higher mineral concentrations, and lower backgrounds.

Aluminum↗
PubMed1979

High yields of coatless spores of Clostridium perfringens strain 8--6 in a defined medium.

Coatless spores of mutant strain 8--6 of Clostridium perfringens were formed reproducibly at levels exceeding 10(7)/mL in a defined medium. Confirming previous observations, the spores are quite stable in water and resistant to heat, octanol, and ethanol. They also resist 5% phenol. Electron microscopy confirms, with further evidence, the probable absence of any structure exterior to the cortex. The levels of sporulation attained are sufficient to permit recovery and purification for future studies on physicochemical and germination properties. The defined medium makes possible studies on spore coat (and exterotoxin) biosynthesis and coat assembly.

Cell Wall↗
PubMed1978

Behavioral toxicity of anesthetic gases.

Operating room personnel were studied for evidence of acute reversible or chronic cumulative cognitive dysfunction as measured by psychometric testing. In comparison with matched controls, no acute reversible deficits were noted in a relatively unpolluted operating room environment. There were only 2 marginally significant test differences between the control and operating room groups; however, control subjects did better than operating room personnel on 16 of 18 tests at both the beginning and end of the work week. Analyses of the deficit patterns and correlations with years of operating room exposure only weakly support the hypothesis that the test differences are due to toxic exposure.

Adult↗
PubMed1978

X-ray microanalysis of epon sections after oxygen plasma microincineration.

Dark-gold sections of osmium tetroxide-fixed, Epon-embedded brown adipose tissue before and after low-temperature oxygen plasma microincineration were examined using a high-resolution scanning transmission electron microscope and an energy-dispersive X-ray spectrometer. Microincineration produced ash patterns which were free of organic matrix, chlorine (from the Epon) and probably osmium (from the fixative). X-ray sensitivity was improved by a factor of 2-4 owing to decreased background, and sulphur, calcium and probably phosphorus were detected in the ash. Fidelity of the ash patterns permitted microanalytical spatial resolution of 0.1 micrometer or better. Oxygen plasma microincineration is thus shown to offer advantages for high resolution X-ray microanalysis of conventionally sectioned biological material. Its future application to shock-frozen, frozen-dried, unstained sections is indicated.

Adipose Tissue, Brown↗
PubMed1976

Improved methods for sampling and analysis of vinyl chloride.

An analytical scheme was developed for vinyl chloride, which is applicable to ambient and in-plant atmospheres. Using computerized gas chromatographs equipped with automatic injection system and flow rate control, high reproducibilities are achieved in the ppb range. Samples from various sources have been analyzed.

Air Pollutants↗
PubMed1975

Computerized gas chromatographic-mass spectrometric analysis of polycyclic aromatic hydrocarbons in environmental samples.

Substantial progress has been made in the last few years in the development of a rapid method for determining polycyclic aromatic hydrocarbons (PAH) in environmental samples. The three-step method consists of (i) a preliminary separation of PAH by solvent and/or column chromatography, (ii) identification by a combination of gas chromatography with quadrupole mass spectrometry and computer, and (iii) measurement by computerized gas chromatography using internal standards. Samples of industrial effluents, coke oven emissions, coal tar and airborne particulates have been investigated. The efficiencies of different gas chromatographic columns were evaluated during these investigations.

Chromatography, Gas↗
PubMed1975

Three common faults in current practice that influence the validity of data obtained from electronic air pollution instrumentation.

Instrumental development is now entering a more logical era, where the former artistic character of electronics is being replaced by cold technology. Because of this, one should be expect more reliability; however, there still exist many weak links in practical application. Digital readout systems and computer processing induce a false sense of security. In reality, it is the sample-measurement relationship that determines an instrument's credibility and not the number of digits on its meter. In describing three faulty practices that greatly influence an instrument's performance, it is hoped that measurement may be more closely related to the sample!

Air Movements↗
PubMed1975

Fibrous dysplasia.

Three cases of monostotic fibrous dysplasia of the cranial bones are presented. Several theories of the etiology of this uncommon condition are put forward and the relationship between monostotic and polyostotic fibrous dysplasia, Albright's disease, and hyperparathyroidism is examined. The difficulty in diagnosis and the ways they may present to the ear, nose and throat surgeon are discussed. It is suggested that conservative surgery is the best mode of treatment for maxillary or temporal lesions. However, ethmoid lesions, particularly when the optic foramen or base of skull are eroded, may need a neuro-surgical approach. The use of radiotherapy in any case is deprecated.

Child↗