Mum In Length Research Articles

High speed cinemicrographic studies on rabbit tracheal (ciliated) epithelia: determination of the beat pattern of tracheal cilia.

High speed cinemicrographs reveal that the ciliary configuration and beat pattern of rabbit tracheal cilia differ significantly from classid descriptions, although the basic forward and return pattern is still observed. The tracheal cilia are short and stout (about 6 mum in length) and are of a slightly bent original configuration bent original configuration. At the start of the forward stroke, the cilia bear about 75-90 degrees to the epithelial surface in the direction of the forward stroke. The forward stroke is planar and consists of a simple "bowing" movement, without showing any progressive bending and without changing the original ciliary configuration. The complete forward stroke sweeps through an arc of about 35-40 degrees, with the tips of the cilia penetrating the bottom of the mucous layer through an arc of about 5-8 degrees at the start of each forward stroke. The return stroke starts from close to the epithelial surface and returns to the starting position of the forward stroke by reversing the planer forward pathway at a reduced speed. The stout nature of the cilia, the original bent ciliary configuration, the near vertical starting position of the forward stroke, the extent of the angular sweeps of the strokes, the peculiar "bowing" forward stroke movement, and the nature of the return stroke all serve to enhance efficiency in moving fluid forward. It has been documented that each forward stroke of the tracheal cilia caused and maintains a swift forward movement of the intermediate serous (liquid) layer of the mucociliary system. This movement, in turn, reacts hydrodynamically with the top mucous layer, and together with the clawing action of the tips of the cilia at the start of the forward stroke, causes the mucous layer to move cephalad in the manner of a conveyor belt.

Transmission and scanning electron microscopy of the human ceruminous apocrine gland. II. Myoepithelial cells.

The myoepithelial cells of the human ceruminous apocrine gland were observed with transmission and scanning electron microscopes. The myoepithelial cells are long fibrous cells about 100-150 mum in length and 3-5 mum in width. They are arranged in parallel with each other, and their long axes are parallel to that of the secretory tubule itself. The tips of cells are often sharply pointed and their lateral tapering surface may be contiguous with adjacent cells forming a side-by-side contact, while other cells may have a blunt tip which is conjuncted with a similar tip of the next cell forming an end-to-end junction. The myoepithelial cells are joined to each other by desmosomes and there are also desmosomes at their junction with secretory cells. The outer surface of the cell abutting on the basal lamina has some exaggerated densities which are undoubtedly identical to the hemidesmosomes of epidermal cells. There are well developed foldings in the plasma membrane of the secretory cells, but the surface of the myoepithelial cells has very few foldings and projections. The relative shortage of intercellular attachment devices between the secretory and myeopithelial cells makes it easy to peel off the secretory cells to disclose the myoepithelium, a useful feature of scanning electron microscopy. The nucleus-containing part of the cell protrudes slightly upward and invades the secretory epithelium. The cytoplasmic rim surrounding the nucleus contains a small Golgi apparatus and some other organelles. The cytoplasm of the basal half of the cell contains closely packed myofilaments running parallel to the long axis of the cell. There is no definite arrangement of thin and thick myofilaments. Microtubules which often occur in pairs are arranged parallel to the myofilaments.

Membrane unbound crystals in pancreatic acinar cells of the mouse.

The exocrine pancreas of normal mice was investigated electron microscopically. The crystals were encountered in the basal cytoplasm of the acinar cells. They exhibited usually rectangular or rhomboidal profiles, measuring less than 5 mum in length and more than 0.1 mum in width. The matrices of these crystals displayed substructures of parallel dense linear pattern. The center-to-center distances between the dense lines were 100 similar to 150 A. The crystals were not limited at their surface by any membrane, but rather were densely circumscribed or sporadically surrounded by ribosomes. Filaments were interposed between ribosomes and crystal matrices and also between matrices of abutting crystals. The significance of the close relation of ribosomes to crystals was discussed.

Electron microscopy of endothelial microvilli of large arteries.

Scanning electron microscopic investigations by others have revealed "hair-like" projections from the endothelial surface of the rabbit aorta. We have confirmed by transmission electron microscopy that endothelial microvilli are found, in a limited number of areas in the aortic arch, particularly at the presumed site of fetal origin of the ductus arterious and near the origin of the subclavian artery. The microvilli are almost uniform in diameter (about 0.1 mum) and are as long as 3 mum in length. The outer leaflet of the limiting membrane shows a fuzzy appearance, and thin filaments are recognized in their interiors. A profuse array of endothelial microvilli was also found over the entire surface of the large arteries of human fetuses. The possible hemodynamic significance of these processes is discussed.

Electron microscope study of native and crosslinked rabbit muscle phosphofructokinase.

Electron microscopy of native and dimethyl-suberimidate crosslinked rabbit muscle phosphofructokinase (EC 2.7.1.11; ATP:D-fructose-6-phosphate 1-phosphotransferase) has been carried out using negative staining with sodium phosphotungstate. The results obtained suggest the protomer of molecular weight 80,000 can be approximated as a prolate ellipsoid with axes of 67 A and 25 A. The dimer, which is the fundamental unit for polymerization, is formed by association along the 25 A axis and has approximately dimensions of 67 A X 55 A X 25 A. The tetramer appears to be formed by an end-to-end aggregation of dimers, and the octamer is a sheet-like structure made up of a side-to-side aggregation of tetramers. Higher crosslinked aggregates and long crosslinked filaments also are seen. The filaments have a constant width of about 250 A, are about 0.5 mum in length, and appear to involve tetramers as a fundamental structural unit. The functional significance of the filament structure is not known.

Asbestos emissions from baghouse controlled sources.

There is virtually no information published on the absolute efficiency of baghouses in reducing the emmisions of fine particles of asbestos. This lack of information is unfortunate because serious occupational health problems may result from the common practice of recirculating air to conserve energy. Emission testing has been conducted at five asbestos processing plants where the emissions are controlled by baghouses. The results showed that the mass removal efficiency frequently exceeded 99.00%. Membrane filter samples of the effluent were examined by optical and electron microscope. It was observed that despite the high mass efficiency, the number of fibers emitted, which were greater than 1.5 mum in length, was about 10(4)-10(5) fibers/m3, while the number of fibers less than 1.5 mum was 10(7)-10(8) fibers/m3. The significance of the size of the fibers in terms of probably health impact is briefly discussed.

Purification and properties of tuberculin-active protein from Mycobacterium tuberculosis.

When Mycobacterium tuberculosis was grown on Sauton medium, intracellular tuberculin-active protein was produced. This product was purified by chromatography on DEAE-cellulose and Sephadex G-200 and was obtained in crystalline form. The crystals were plates, somewhat irregular in shape, about 50 mum in length and 25 mum in width. The yield corresponded to a 1.5% over-all recovery of total protein. Ultracentrifugal analysis showed only one major component with a calculated molecular weight of 9700. Sedimentation velocity analysis gave a sedimentation coefficient at 20 degrees (see article) of 1.73 S. The estimated specific activities of tuberculin-active protein were 6.33 times 10-9 tuberculin units per mg of protein-nitrogen for sensitized guinea pigs and 6.33 times 10-11 tuberculin units per mg of protein-nitrogen for humans. This is the most potent tuberculin-active protein that has yet been obtained.

The basal apparatus. Mass isolation from the molluscan ciliated gill epithelium and a preliminary characterization of striated rootlets.

The basal apparatus, consisting of an array of interconnected basal bodies bearing bifurcating striated rootlets encompassing a nucleus, has been isolated from hypertonically deciliated columnar gill epithelial cells of the bay scallop Aequipecten irradians through gentle lysis with Triton X-100. The rootlets, 8-10 mum in length, were not easily preserved with conventional electron microscope fixatives, suggesting that the extent of their contribution to cellular architecture has been somewhat underestimated, even though Englemann described many of the structural details of the basal apparatus in 1880. The striated rootlets were soluble at high but not at low pH, in 2 M solutions of sodium azide and potassium thiocyanate but not sodium or potassium chloride, in 1% deoxycholate but not digitonin, and in the denaturing solvents 6 M guanidine-HC1, 8 M urea, and 1% sodium dodecylsulfate at 100 degrees C. The protein found consistently when rootlets were solubilized migrated on SDS-polyacrylamide gels as a closely spaced doublet with apparent molecular weights of 230,000 and 250,000 daltons. This unique protein, distinct from tropocollagen or various muscle components, has been named ankyrin because of the rootlet's anchor-like function in the cell.

Molecular weight of RNA subunits of Rous sarcoma virus determined by electron microscopy

Secondary cultures of chicken embryo fibroblasts were infected with the Schmidt Ruppin strain of Rous sarcoma virus (RSV). Five days after infection, the medium was replaced at 2-h intervals with phosphate-free Eagle medium containing 50 muCi of [32P]orthophosphate per ml. Virus was collected by centrifugation, and the RNA was extracted and denatured with dimethyl sulfoxide, and the 33S subunit RNA was isolated by sucrose gradient centrifugation. The molecular weight of the RSV subunit RNA was determined by length measurement in the electron microscope, by using bacteriophage MS2 RNA as a length marker. Molecules of between 2.5 and 3.3 mum in length made up over 50% of the subunit RNA preparation. In this paper, we define RSV RNA subunits as that RNA released from the 70S RNA complex by dimethyl sulfoxide treatment, which sediments as a peak at 33S. Assuming the molecular weight of MS2 RNA to be 1.2 times 10-6, we calculate the molecular weight of RSV subunit RNA to be 3.12 times 10-6 plus or minus 0.25 times 10-6.

Hammondia hammondi gen. nov., sp.nov., from domestic cats, a new coccidian related to Toxoplasma and Sarcocystis.

Hammondia hammondi gen.nov.,sp.nov (Eimeriorina:Sarcocystidae) is described as an obligate heteroxenous protozoon of domestic cats (final host) and laboratory mice (experimental intermediate host). Oocysts from the final host are infectious only for the intermediate host; and cysts from the intermediate host are infectious only for the final host. Intracellular cysts develop principally in striated muscle of mice that ingest oocysts, with a few cysts in the brain and perhaps elsewhere. Cysts are without septa or radial spines; bradyzoites are slender, there is no evidence of metrocytes. Cysts are not infectious for mice. After the ingestion of cysts by cats, a multiplicative cycle precedes the development of gametocytes in the epithelium of the samll intestine. Oocysts are shed unsporulated, sporogony is outside of the host, resulting in two sporocysts with four sporozoites each. Oocysts of the species average 11 x 13 mum. The prepatent period i 5s 5 to 8 days, and oocyst shedding persists for 10 to 28 days followed by immunity. Cysts in skeletal muscle measured between 100 and 340 mum in length and 40 and 95 mu-m in width. Experimental intermediate hosts are laboratory mice, rats, hamsters, guinea pigs, Peromyscus and Mastomys. Some of the intermediate hosts develop low levels of antibody and some cross-immunity against Toxoplasma; however, this has not been observed in cats.

Tumorigenic effect of fibrous dust in experimental animals

Fibrous dusts (chrysotile, glass fibers, nemalite, palygorscite, and gypsum) and granular dusts (actinolite, biotite, hematite, pectolite, sanidine, and talcum) were injected intraperitoneally into rats. The fibrous dusts (other than gypsum) resulted in a high incidence of mesothelioma (30 - 67%). Gypsum produced only 5% and granular dusts none at all. It is suggested that the fibrous shape leads to a high multiplication rate of cells and predisposes to tumor formation. Fibrosis, in the other hand, does not so predispose. Milled chrysotile with 99.8% fibers than 5 mum in length are carcinogenic in our experience. The carcinogenicity of glass fibers in our experiments may have significance for occupational situations.

The movement of optically detectable organelles in myelinated axons of Xenopus laevis.

1. Intra-axonal organelles were detected by darkfield and Nomarski microscopy in isolated myelinated nerve fibres from Xenopus laevis. Nerve fibres from the 8th spinal roots, the sciatic nerve, and identified motor and sensory axons from other hind limb nerves were used. The movement of the organelles was recorded either on motion picture film or by noting the times at which they crossed the lines of an ocular grid.2. Three groups of organelles were detected in all fibres. A group of particles with round profiles 0.2-0.5 mum in diameter moved somatopetally. Another group of round particles moved somatofugally. The ratio of the number of somatopetally travelling particles to the number of somatofugally travelling particles was about 10:1. The third group of organelles consisted of rod-shaped bodies about 0.2-0.3 mum in diameter and 1-8 mum in length; these were usually stationary.3. All the round particles appeared to move independently of each other with a saltatory motion. The somatopetally and somatofugally travelling particles had statistically different mean velocities of 0.98 and 1.32 mum/sec respectively.4. Round particles often crossed the node of Ranvier with no appreciable change in velocity. Some, however, were temporarily arrested at the entrance to the node.5. While the rod-shaped organelles were usually stationary, they occasionally moved rapidly lengthwise for distances of up to 10 mum. Rarely a rod-shaped organelle exhibited a continuous saltatory motion.6. Round particles often travelled in either direction along the edge of rod-shaped organelles. One rod was observed to move along the path previously taken by a round particle.7. The findings are discussed with respect to (a) the normality of the preparations, (b) the numbers of particles travelling in each direction, (c) the nature of the organelles, and (d) the mechanisms underlying the motion.8. We suggest that particles move along microtubules which have specific directionalities and particle affinities. The microtubules are in bundles and are closely associated with rod-shaped mitochondria.

Slow Conduction in Cardiac Muscle: A Biophysical Model

Mechanisms of slow conduction in cardiac muscle are categorized and the most likely identified. Propagating action potentials were obtained experimentally from a synthetically grown strand of cardiac muscle (around 50 mum by 30 mm) and theoretically from a one-dimensional cable model that incorporated varying axial resistance and membrane properties along its length. Action potentials propagated at about 0.3 m/s, but in some synthetic strands there were regions (approximately 100 mum in length) where the velocity decreased to 0.002 m/s. The electrophysiological behavior associated with this slow conduction was similar to that associated with slow conduction in naturally occurring cardiac muscle (notches, Wenckebach phenomena, and block). Theoretically, reasonable changes in specific membrane capacitance, membrane activity, and various changes in geometry were insufficient to account for the observed slow conduction velocities. Conduction velocities as low as 0.009 m/s, however, could be obtained by increasing the resistance (r(i)) of connections between the cells in the cable; velocities as low as 0.0005 m/s could be obtained by a further increase in r(i) made possible by a reduction in membrane activity by one-fourth, which in itself decreased conduction velocity by only a factor of 1/1.4. As a result of these findings, several of the mechanisms that have been postulated, previously, are shown to be incapable of accounting for delays such as those which occur in the synthetic strand as well as in the atrioventricular (VA) node.

Vacuum probe: new approach to the microbiological sampling of surfaces.

The need for a device to sample large areas that are lightly contaminated with microorganisms motivated the development of the vacuum probe. The intended use of the instrument is to sample clean surfaces in laminar flow clean rooms, but the device could be used for sampling surfaces in other clean environments. Such a device was designed, fabricated, and tested at Sandia Laboratories, Albuquerque, N.M. In these tests, the vacuum probe removed a mean of 89% and assayed a mean of 67% of bacterial spores, approximately 1 mum in length, settled on smooth surfaces which were free from viscous films.

Vacuum Probe: New Approach to the Microbiological Sampling of Surfaces

The need for a device to sample large areas that are lightly contaminated with microorganisms motivated the development of the vacuum probe. The intended use of the instrument is to sample clean surfaces in laminar flow clean rooms, but the device could be used for sampling surfaces in other clean environments. Such a device was designed, fabricated, and tested at Sandia Laboratories, Albuquerque, N.M. In these tests, the vacuum probe removed a mean of 89% and assayed a mean of 67% of bacterial spores, approximately 1 mum in length, settled on smooth surfaces which were free from viscous films.