Sieving Behavior Research Articles

Histamine decreases selectivity of sheep lung blood-lymph barrier.

Histamine increases lymph flow and protein flux from the sheep lung. This increase in water and protein movement has been attributed to an increase in lung microvascular permeability-surface area product caused by histamine. Whether it was permeability that was changed or whether it was surface area cannot be discerned from past work. Histamine might increase either of these determinants of transport in the sheep lung. Previous measurements of several plasma protein fractions in plasma and lymph showed no change in the sieving behavior of the microcirculation with intravenous histamine, suggesting that only surface area was changed. In the present study, even larger test molecules were used to probe the limits of transport through the lung's blood-lymph barrier. Fluorescein isothiocyanate-labeled dextrans (FITC-dextran) that can normally permeate lung lymph do so more readily after intravenous histamine infusion (3 micrograms X kg-1 X min-1). Formerly impermeable FITC-dextran fractions also appear after histamine administration. No definitive size limit to the transport of dextran was found in histamine-stimulated sheep lungs. Intra-arterial histamine does not increase lung lymph, protein, or FITC-dextran flow. These results suggest that histamine changes the permeability or sieving characteristics of the lung microvascular barrier making it less size selective to large molecules. Surface area for transport may also increase.

Zeolite inclusion complexes

Zeolites provide the largest and most useful family of porous host crystals, stable in the presence or absence of guest molecules. An account is given of their structural characteristics in terms of intracrystalline channels and cavities of molecular dimensions; their total intracrystalline pore volumes; and the intracrystalline distribution patterns of guest molecules, often present as clusters or filaments. The way in which the shape and size of the molecules relate to the shape and size of the apertures or windows giving access to the cavities, together with other factors such as cation location, then determine molecule sieving behaviour, which is discussed with reference to several types of zeolite sieve. The relation between diffusivity and molecular dimensions is also illustrated. A comparison between zeolites and clathrate host lattices shows that there are strong similarities of several kinds. Zeolites may form inclusion complexes with metals, salts and polar or non-polar molecules, examples of which are briefly considered, together with isotherms for some of these types of complex. An account of equilibrium and its formulation demonstrates the thermodynamic background and illustrates the degree of success which has been obtained in describing isotherms in terms of various models.

Zeolite sorbents. Modification by impregnation with salts

A study has been made of the effect of salt inclusion in certain zeolites upon the kinetics of sorption of, and the molecule sieving behaviour shown towards, n-hexane, 2- and 3-methyl pentanes, 2,2- and 2,3-dimethyl butanes, cyclohexane and benzene. The zeolites selected provided three typical one dimensional channel systems. They were zeolite L, offretite and H-mordenite. The salts used to impregnate the channels were KCl, KBr, K2SO4 and K2CrO4, all comparatively stable to heating. The effects of salt concentration and salt type were investigated in each zeolite and also of washing and extraction of salt-impregnated sorbents. Among the above salts K2CrO4 gave the largest effects. Access to the channels could be selectively controlled and changed by salt imbibition giving rise to various separation possibilities based on differences in size and shape of sorbate molecules.

The effects of pre-test conditions on social facilitation of drinking in ducks

The drinking and sieving of Khaki Campbell ducklings have been used as suitable behaviour patterns with which to study the social interactions in flock-living birds. Duckling from four-bird flocks were deprived of water for 3 hr, either in isolation or in groups of four. When the flocks were allowed access to water it was found that the isolated ducklings drank less than the non-isolated ducklings. Whilst both deprived and non-deprived birds engaged in sieving activity during the test, the sieving movements of the non-deprived birds were of longer duration than those of the deprived birds. Pre-test isolation of flock members was also shown to increase the duration of sieving movements. Re-introducing the isolated ducklings to each for the last 5 min of deprivation failed to eliminate the difference in either the drinking or the sieving behaviour between the isolated and non-isolated birds. The difference in drinking, but not sieving, could be eliminated by reuniting the birds for the last 30 min of deprivation. The disruption of flock ‘cohesion’ may lead to the failure of the mechanism of social facilitation despite a similar motivational condition in all flock members.

Sieving Behavior of a Series Membrane System

Sieving Behavior of a Series Membrane System