Low-viscosity Medium Research Articles

Shear viscosity of settling suspensions

A new apparatus is presented which allows the determination of the viscosity of suspensions of high density particles in low viscosity media. Results obtained on suspensions of low density particles compare well with those obtained on a Weissenberg Rheogoniometer equipped with a cone-and-plate and a bob-and-cup. Also, a very interesting observation is that the Eilers equation, conveniently modified to take into account the shape of the particles by means of the intrinsic viscosity, can well correlate all the data.

Fine structural changes in the mandibular gland of the male spider crab, Libinia emarginata (L). Following eyestalk ablation.

Mandibular glands from destalked male spider crabs were fixed in glutaraldehyde-paraformaldehyde, post-fixed in 1% osmium in phosphate buffer, dehydrated in acetone and embedded in Spurr's low-viscosity medium ('69). The glands hypertrophy and several changes occur in the subcellular cytoarchitecture following eyestalk ablation. These include loss of most of the smooth endoplasmic reticulum or its appearance as lamallae, appearance of numerous polysomes and a change in mitochondrial structure. Large vesicles with ribosomes spaced at intervals along their membranes are apparently formed by blebbing of the outer nuclear membrane and appear throughout the cytoplasm. Banded structures consisting of alternate granular and flocculent materials are found within the nucleus.

The kinetics of extraamniotically injected prostaglandins to induce midtrimester abortion

In an attempt to improve the extraamniotic administration of prostaglandins in effecting abortion, the movement of injected prostaglandins in a high or low viscosity medium has been observed by radiological studies and radioimmunoassay of PGE and PGFα in amniotic fluid and maternal plasma in association with intrauterine tocographic responses. Results obtained suggest that the immediate response by the uterus is a reflection of the speed of absorption of prostaglandins from the chorio-decidual space and that this influences the outcome in inducing abortion within 24 hours. By giving the prostaglandins in a viscous medium a slower release of prostaglandins was produced in most cases, which probably accounts for the greater efficacy obtained using single injections of prostaglandins in this vehicle compared with normal saline.

Bacterial flagella rotating in bundles: a study in helical geometry.

Bacterial flagella are semi-rigid helices that undergo true rotation. In peritrichously flagellated bacteria (e.g., Escherichia and Salmonella) there are many flagella on each cell; during translational cell movement these operate as a coordinated bundle that actively disperses upon reversal of the rotation sense. The dynamic behavior of a set of helices originating on separate rotational axes is explored by a working model, geometrical analysis, and hydrodynamic calculations. A critical relationship exists between the interaxial separation and phase difference of parallel helices with overlapping domains; in the subcritical case the filaments are not intertwisted, whereas in the supercritical case they are intertwisted in the same sense (left-handed) as the helices, with one twist per helical turn. During counter-clockwise rotation (the sense operative in forward swimming) any preexisting twists of this kind are automatically cancelled and the helices brought progressively into phase. Hydrodynamic calculations suggest that some wrapping then occurs in a right-handed sense, opposite to that of the helices; this necessitates a distortion from true helical geometry which is minimized by maintaining a coaxial in-phase relationship. A highly coordinated helical bundle results that is capable of operating smoothly for an indefinite period, in agreement with the observed behavior of swimming bacteria. During reverse rotation, the supercritical case develops to cause jamming of the bundle, as has been observed with bacteria in high-viscosity medium. The explosive dispersal of the bundle during reversal in low-viscosity medium is a consequence of a complicating phenomenon, namely, a drastic change in flagellar quaternary structure. The overall conclusion is that bundle formation and function are perfectly compatible with a rotational mechanism for the individual flagella.

Isopycnic centrifugation of mammalian metaphase chromosomes in metrizamide

Isopycnic centrifugation is a powerful separation technique, but when applied to metaphase chromosome research it has been technically frustrating. High concentrations of salt rapidly dissociate metaphase chromosomes, and MacGillivray, et al. [l] show that high concentrations of salt dissociate nucleoproteins. Chromatin will band isopycnically in CsCl after fixation with formaldehyde [2], but the reaction is irreversible and the material of little use thereafter. Obviously, formaldehyde treated chromosomes are equally useless. We have used sucrose, Ficoll, and fructose as the support media for isopycnic banding of metaphase chromosomes, but at the density required to band the chromosomes (p=l.3 1 g/cm3) the viscosity of the sugar solutions is so high as to make their use prohibitive. Chromatin has been shown to band in chloral hydrate gradients [3], but these gradients are very difficult to handle and are also quite viscous which again make them unsuitable for banding metaphase chromosomes. In order to circumvent these problems an elaborate system of nonaqueous gradients was developed by Stubblefield and Wray [4] for buoying chromosomes. These organic gradients accomplish their objective of isopycnically banding metaphase chromosomes co= 1.36 g/cm3) in a low viscosity media. However, the technical problems in preparing these gradients, the solvent properties of the organic chemicals and especially their ability to extract certain proteins from the chromosomes make this system amenable only to certain specified applications. The introduction of iodinated density gradient media for biological separations represents a signifi-

Light‐Induced Body Movement of Euglena gracilis Coupled to Flagellar Photophobic Responses by Mechanical Stimulation*†

SYNOPSIS. In low viscosity media, Euglena gracilis strain Z responds to a sudden change in light intensity by a cessation of forward movement, followed by a reorientation of the locomotor flagellum which results in turning of the cell around the lateral axis (photophobic response). At a viscosity interface between low [∼ 1 cP (centipoise)] and high (4000 cP) media, the cells exhibit avoidance responses or become immobilized in the higher viscosity medium. Upon changing the light intensity, free swimming cells have photophobic responses, while immobilized ones undergo body contractions. For cells immersed in media of varying viscosity, the delay between light stimulation and body contraction (transduction time) is shortest at high viscosities. From 500 to 2000 cP, where the cells are capable of both movement and light‐induced body contractions, there is a logarithmic dependence of the transduction time on the viscosity. The transduction time does not vary appreciably with the intensity of the primary light stimulus within a range of 0.14‐1.13 kW/m2.

Theoretical model for diffusion controlled reactions of solvated electrons, incorporating a tunnelling mechanism

The effect on diffusion-controlled reactions, of electron tunnelling from a solvent cavity to a scavenger molecule, is examined. The radial diffusion equation is modified to include a sink term, which varies exponentially with distance from the origin, and thus simulates tunnelling behaviour. An analytical solution is obtained for the steady-state, and applied to diffusion controlled reactions of the solvated electron in media covering a wide range of viscosities. In low viscosity media (η∼10–3 kg m–1 s–1) reaction can take place at a reactant separation of about two molecular diameters, this distance increases with viscosity, reaching about eight molecular diameters for η= 109 kg m–1 s–1. The theory is also applied to energy transfer by an exchange mechanism; transfer only begins to take place from distances greater than the encounter distance when the viscosity reaches ∼105 kg m–1 s–1.

Spherical sound-wave diffraction by a sphere in a viscous medium

The problem of spherical sound-wave diffraction by a sphere in a viscous medium is discussed. Applying the method of separation of variables, we obtained exact formulas for the hydrodynamic field elements in a low-viscosity medium. Furthermore, by applying the Morse [1, 2] and Watson [3] method to the exact formulas, we determined asymptotic formulas for the same quantities in the case of long and shortwave propagation.

A New Myxosporidan in Red and Golden Shiners

Myxosoma cyprini sp. n. is described in the gills of the red shiner, Notropis lutrensis, and golden shiner, Notemigonus crysoleucas, from Oklahoma. Cysts measuring 0.3 ua or less occur adjacent to capillary endothelial cells of secondary gill lamellae. Infected fish were collected in October 1971 and in June 1972. M. cyprini is disporoblastic and development is asynchronous. Mature spores are pyriform in front view and lenticular when viewed from the side. Fresh spores average 14.4 A in length by 8.0 uL in width by 7.5 u in thickness. Polar capsules are pyriform and 7.1 u long by 3.0 u wide. Approximately 9 windings of the polar filaments are seen inside each capsule. Extruded polar filaments are 100 to 110 A long. Mucous envelopes are present. All of the 35 red shiners and 9 of 10 golden shiners contained M. cyprini. Host reactive cells do not appear at the locus of the parasite. A new species of Myxosoma was found in the branchial tissues of two cyprinoid fishes, the red shiner, Notropis lutrensis, and the golden shiner, Notemigonus crysoleucas. Immature and mature stages of the parasite are described herein. The specific name M. cyprini, referring to the hosts' family name, is proposed. MATERIALS AND METHODS Twenty-two red shiners were collected by seining Little Stillwater Creek, Payne County, Oklahoma, on 2 October 1971. Thirteen more red shiners and 10 golden shiners were collected from the same site on 8 June 1972. Portions of infected gills were macerated in water on glass slides or were fixed for 4 to 16 hr in a cold 2% glutaraldehyde solution containing 0.5% acrolein, 4.0 mM calcium chloride, and buffered by 0.2 M sodium cacodylate to pH 7.4. Fixed tissues containing the parasite were washed in cold 0.22 M sucrose in the cacodylate buffer and either examined as squashed preparations with phase contrast (Zeiss system) or embedded for sectioning. The embedding steps included postfixation for 30 min in 2% Os04 in the cacodylate buffer, dehydration in a graded ethanol series, and infiltration in Spurr's low-viscosity medium (hard formula; Polysciences, Industrial Park, Warren, Pennsylvania). The embedment was polymerized at 37 to 40 C for 4 hr and 64 to 70 C for 6 to 7 hr. Sections, 1 /t thick, were cut with glass knives on a Porter-Blum MT-2 ultramicrotome, mounted on glass slides, and stained on a hot plate with 0.5% toluidine blue in 1% sodium borate. Stained sections were rinsed in running water, air-dried, flooded with immersion oil, and cover-slipped. Observations of stained sections were made by both bright-field and phasecontrast optics using 125 to 2,500X magnification. Mucous envelopes were demonstrated in fresh spores by the method of Lom and Vavra (1963). Received for publication 18 July 1973. Description of the sporogenic stages and spores is based on composite findings in both fresh and fixed unstained smears. Description of the plasmodium and of its spatial relationship to host tissues is based on observations of sectioned and