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Biomedical subjects

J W Clark

Publications and source records attributed to J W Clark.

At least 199 records · Page 11Linked to original sources
PubMed1972

Separation of Treponema pallidum from tissue substances by continuous-flow zonal centrifugation.

The zonal ultracentrifuge was used for separation of Treponema pallidum from large volumes of rabbit testicular syphiloma extracts by continuous-flow centrifugation in a cesium chloride density gradient. The gradient was linear with radius from a density of 1.05 to 1.36 g/ml. Operating speeds were 15,000 rev/min for the continuous-flow phase and 25,000 rev/min for a 30-min banding period. A total of 9 x 10(9) (24.3%) treponemes were recovered from the original extract. Of the treponemes recovered, 88% formed a band at a density of 1.170 to 1.211 g/ml. Within the limits of present methods of assay, these fractions were relatively free from testicular particulates and protein when compared with treponemes recovered after differential centrifugation. Observations of the isolated fractions by dark-field and electron microscopy indicated a lack of gross morphological damage to T. pallidum. Their antigenic characteristics were also retained, as evidenced by their ability to react with syphilitic sera in the indirect fluorescent-antibody procedure.

Animals↗
PubMed1971

Fiber interaction in a nerve trunk.

This paper is concerned with the nature of the transmembrane potential induced in an inactive nerve fiber lying in an impressed potential field within a nerve trunk. The impressed potential field is assumed to be produced by the synchronous activity of other fibers within the trunk; an expression for the induced transmembrane potential is obtained utilizing the principles of electromagnetic field theory. The results strongly indicate that membrane capacitance is the main determinant of the induced transmembrane potential wave form.

Action Potentials↗
PubMed1970

A mathematical study of nerve fiber interaction.

This paper presents a quantitative description of the electric field interaction between two adjacent unmyelinated nerve fibers (one active, the other inactive) for the infinite medium and nerve trunk geometries, and considers their dependence on various electrical and geometrical parameters. Based on the use of synthetic giant axon data, the conclusion of this study is that the cross-sectional area of the nerve trunk and the specific resistivity of the interstitial medium are of particular importance to the degree of fiber interaction. Other factors such as separation distance between fibers, axoplasmic resistivity, membrane resistance, and capacitance of the inactive fiber, are also investigated and found to be of secondary importance.

Action Potentials↗
PubMed1970

Passage of Treponema pallidium through membrane filters of various pore sizes.

The passage of Treponema pallidum through commercially available Millipore membrane filters of various pore sizes was examined. No microscopically detectable organisms passed through a filter with a pore diameter of 0.22 mum. As pore size was increased, progressively more organisms passed through. Motile organisms passed through filters to a greater extent than nonmotile ones; however, 22% of the motile and 50% of the nonmotile T. pallidum organisms did not pass through the largest pore diameter tested (14.0 mum). Filtration of T. pallidum suspensions through membrane filters may offer a way of separating the organisms from larger particles of debris which accompany their extraction from rabbit testicular syphilomas.

Animals↗
PubMed1970

Membrane filtration of the Reiter treponeme.

A membrane filtration technique with commercially available membrane filters (Millipore Corp.) was effective for the removal of Reiter treponemes from liquids such as fluorescent-antibody conjugates, to which the organisms are added for adsorption. Reiter treponemes from an 8-day culture were not microscopically detectable in filtrates through membranes with a pore diameter of 0.45 mum, but treponemes were demonstrated in the filtrate by cultural methods. No organisms of the 8-day culture passed through a membrane filter having a pore size of 0.22 mum, as determined by microscopy and culture. Culture data indicated that a filter with a pore size of 0.1 mum was necessary to prevent passage of treponemes from 4-day cultures. It is recommended that a membrane filter with a pore size of 0.22 mum or smaller be used for the removal of Reiter treponemes from suspensions and that the age of the culture be considered in choosing filter pore size.

Culture Media↗
PubMed1969

Statistical approach to evaluating the method of Morgan and Vryonis for enumerating Treponema pallidum.

The contributions of four components to the error in the microscopic enumeration of spirochetes (Treponema pallidum) by the method of Morgan and Vryonis were determined. Where N(s) = the number of slides counted, N(r) = the number of recounts of 50 fields per slide, N(p) = the number of pipettes used, and N(e) = the total number of counts of 50 fields made, the coefficient of variation is 2 times the square root of (17.5(2)/N(s) + 18.6(2)/N(r) + 14.8(2)/N(p) + 6.1(2)/N(e)) with 95% confidence.

Analysis of Variance↗