Carcinogenicity of the insulation wools: reassessment of the IARC evaluation

In assessing the health evidence concerning man-made mineral fibers, the chemical composition, surface activity, durability, and size of fibers have to be taken into account. Special-purpose fine glass fibers need to be separated from the insulation wools (glass, rock, and slag wool). The epidemiological evidence is sufficient to conclude that there has been no mesothelioma risk to workers producing or using glass wool, rock wool, or slag wool. The epidemiological studies have been large and powerful, and they show no evidence of a cause-effect relationship between lung cancer and exposure to glass wool, rock wool, or slag wool fibers. There is some evidence of a small cancer hazard attached to the manufacturing process in slag wool plants 20 to 50 years ago, when asbestos was used in some products and other carcinogenic substances were present. However, this hazard is not associated with any index of exposure to slag wool itself. Animal inhalation studies of ordinary insulation wools also show that there is no evidence of hazard associated with exposure to these relatively coarse, soluble fibers. The evidence of carcinogenicity is limited to experiments with special-purpose fine durable glass fibers or experimental fibers, and only when these fibers are injected directly into the pleural or peritoneal cavity. Multiple chronic inhalation studies of these same special-purpose fine glass fibers have not produced evidence of carcinogenicity. It is suggested that the present IARC evaluation of the carcinogenic risk of insulation wools should be revised to Category 3: not classifiable as to carcinogenicity to humans.

Revision of Australasian Trissolcus species (Hymenoptera : Scelionidae)

The species of Trissolcus Ashmead of the Australasian region (including New Guinea, the Bismark Archipelago and the Solomon Islands to Tahiti and New Zealand) are revised. Trissolcus ancon, T. arctatus, T. cirrosus, T. maori, T. personatus, T. setifer, T. sipioides and T. strigis are described as new. Trissolcus eetion (Dodd), T. egeria (Dodd), T. ephyra (Dodd), T. euander (Dodd), T. flaviscapus Dodd, T. latisulcus (Crawford), T. mitsukurii (Ashmead), T. oedipus (Dodd), T. oeneus (Dodd), T. oenone (Dodd), T. ogyges (Dodd) and T. painei (Ferrière) are redescribed. Trissolcus basalis (Wollaston) is a widely introduced Afrotropical species found throughout this region. The following new synonymies are proposed: Trissolcus coriaceus Dodd, 1915 = T. egeria (Dodd), 1914; T. oecleus (Dodd), 1913, T. darwinensis (Dodd), 1914, T. erigone (Dodd), 1914, T. banksi (Gahan), 1921 and T. priapus (Nixon), 1938 = T. latisulcus (Crawford), 1913; T. oecleoides (Dodd), 1914 = T. mitsukurii (Ashmead), 1904; T. obliteratus (Dodd), 1914, T. otho (Dodd), 1914, T. biproruli (Girault), 19262, and T. wilsoni (Dodd), 1930 = T. oenone (Dodd), 1913; T. oreas (Dodd), 1913, T. orontes (Dodd), 1914, T. atriscapus (Girault), 1926a and T. beenleighi (Girault), 1932 = T. ogyges (Dodd), 1913.

Epithelial progenitor cells in the rat trachea

Highly pure populations of basal and secretory cells from the rat trachea have been inoculated into denuded tracheal grafts to determine the differentiation pathways of these two cell types. The basal cell inoculum resulted in an epithelium comprised of only basal and ciliated cells, while the secretory cell inoculum gave rise to an epithelium comprised of secretory, basal, and ciliated cells. These results show that, in the rat trachea, the secretory cell is the major progenitorial cell type and the basal cell has only limited progenitorial capacity.

Proliferative responses of rat nasal epithelia to ozone

The epithelium of the female Fischer 344/N rat anterior nasal cavity was examined and found to be composed of four types of epithelia: squamous, ciliated respiratory, nonciliated cuboidal/transitional, and olfactory. DNA replication in these tissues was monitored by bromodeoxyuridine (BrdUrd) incorporation. Labeled cells were identified using a monoclonal antibody recognizing BrdUrd. Ciliated respiratory, nonciliated cuboidal/transitional, and olfactory epithelia from control animals had a low level of DNA replication (1 labeled cell/mm basal lamina); in contrast, the squamous epithelium contained 40 labeled cells per millimeter basal lamina. Female Fischer 344/N rats were exposed to 0.0, 0.12, 0.27, or 0.8 ppm ozone, 6 hr/day for up to 7 days. Observations were made after 3 or 7 days of exposure and after 3 or 7 days of recovery from the 7-day exposure. Following exposure to 0.8 ppm ozone, a transient but marked increase in DNA replication was seen in the nonciliated cuboidal/transitional, while in ciliated respiratory and olfactory epithelia the transient increase in DNA replication was less marked. This increase was prominent after 3 days of exposure and absent by 7 days of exposure in all but the cuboidal/transitional epithelium. Exposure to 0.8 ppm ozone for either 3 or 7 days resulted in hyperplasia of the cuboidal epithelium. A depressed level of DNA replication was seen in the squamous epithelium following 7 days of recovery from 7 days of ozone exposure to 0.8 ppm ozone. This study shows that there are regional differences in DNA replication within the anterior nasal epithelium of the rat and that these levels are modulated by exposure to irritants. The cuboidal/transitional epithelium was the most responsive epithelial cell type to the effects of ozone exposure and may, therefore, provide a sensitive indicator of irritant damage to the respiratory tract.

On time differences in searching for letters in words and nonwords: do they emerge during the initial encoding or the subsequent scan?

Krueger (1970a, 1970b, 1982) has demonstrated that subjects can search for target letters within words faster than they can complete an equivalent search through nonwords, and he further demonstrated that the effect did not arise during the comparison stage. The present study involved three experiments in which the usual word advantage disappeared either when subjects knew where within a display the target item would appear (i.e., it was always the first letter), or when all the component letters were encoded into memory before the task began (i.e., a memory-search task). These data, in conjunction with Krueger's, where interpreted as localizing at least one (and possibly the only) source of the word-nonword difference in this task to the events that occur during the item-to-item transitions subjects make when scanning the letter arrays. That is, these transitions are faster for words than nonwords, and it was suggested that the time difference may emerge because although all the letters from within a word appear to be available in memory before the scan begins, this seems not to be true for consonant arrays. Given that this is the case, part of the word-nonword difference may be attributable to subsequent encoding events that would be needed for the consonant arrays as the scan moves from letter to letter.

Separation and characterization of basal and secretory cells from the rat trachea by flow cytometry

Basal and secretory cells have been separated as highly enriched viable populations from single-cell suspensions of rat tracheal epithelial cells. Isolation of the populations was achieved by preparation of a cell suspension and separation by flow cytometry using contour maps generated from 2 degrees and 90 degrees light scatter signals. Flow cytometric analysis of cells showed 10% of the whole preparation were cells in SG2M phase of the cell cycle. The secretory cells accounted for 86% of these cycling cells; the remainder were accounted for by the basal cells. Culture of sorted populations of basal and secretory cells in serum free defined medium showed that basal cells had a lower (0.6%) colony-forming efficiency than secretory cells (3.4%). Significant differences in blue auto-fluorescence, Hoechst 33342 uptake, and lectin staining were apparent between basal and secretory cells. These results suggest that the secretory cell rather than the basal cell is primarily the cell type involved in maintenance of the normal tracheal epithelium. Secretory cells are greater in number, have a higher proliferative potential, and greater metabolic capability. Because of these traits they may be a critical cell at risk from damage by environmental agents.

The induction of chromosome damage in CHO cells by beryllium and radiation given alone and in combination

Studies were conducted to determine the effects of BeSO4 or X rays, alone and in combination, on cell cycle kinetics, cell killing, and the production of chromosome aberrations in Chinese hamster ovary (CHO) cells. The concentration of BeSO4 required to kill 50% of CHO cells exposed to BeSO4 for 20 h was determined to be 1.1 mM with 95% confidence intervals of 0.72 to 1.8 mM. During the last 2 h of the 20-h beryllium treatment (0.2 and 1.0 mM), cells were exposed to 0.0, 1.0, or 2.0 Gy of X rays. Exposure to either BeSO4 or X rays produced a change in cell cycle kinetics which resulted in an accumulation of cells in the G2/M stage of the cell cycle. However, combined exposure to both agents resulted in a block similar to that observed following exposure to X rays only. The background level of chromosome damage was 0.05 +/- 0.015 aberrations/cell in the CHO cells. Seven hours after the end of exposure to 0.2 and 1.0 mM beryllium, 0.03 +/- 0.003 and 0.09 +/- 0.02 aberrations/cell, respectively, were observed. The data for chromosome aberrations following X-ray exposure were fitted to a linear model with a coefficient of 0.14 +/- 0.01 aberrations/cell/Gy. When beryllium was combined with the X-ray exposure the interactive response was predicted by a multiplicative model and was significantly higher (P less than 0.05) than predicted by an additive model. The influence of time after radiation exposure on the interaction between beryllium and X rays was also determined. No interaction between beryllium and X-ray exposure in the induction of chromosome-type aberrations (P greater than 0.05) was detected. The frequency of chromatid-type exchanges and total aberrations was significantly higher (P less than 0.05) in the radiation plus beryllium-exposed cells when compared to cells exposed to X rays only, at both 9 and 12 h after X-ray exposure. These data suggest that the multiplicative interaction may be limited to cells in the S and G2 stages of the cell cycle.

Inhaled cigarette smoke induces preneoplastic changes in rat tracheal epithelial cells

Rats were exposed 6 h/day, 5 days/week for 5 weeks to levels of cigarette smoke designed to deposit amounts of particulate per gram of lung similar to those experienced by a heavy smoker. Tracheal epithelial cells were isolated and examined in culture for the presence of preneoplastic variants. Two- to three-fold increases in the frequency of variants were observed in cells isolated from smoke-exposed animals compared to those from air-exposed controls. These results provide an estimate of the frequency of cigarette smoke-induced initiation events in respiratory epithelium that will be useful in further defining the role of cigarette smoke in the development of lung cancer.

On the role of word frequency in the detection of component letters

The experiments reported in this study were conducted to explore the issue of race models versus holistic models of word processing. In both types of model, it is assumed that an available word-level encoding for a display will conceal letter information, and thereby inhibit component-letter detection. However, whereas in holistic models it is assumed that encoding always should occur at the word or pattern level first, in the race models it is assumed that encoding occurs at all levels (e.g., feature, letter, and word) simultaneously, with the final level of encoding being at whatever level has been completed first. If the rate of word-level encoding is facilitated by increasing word frequency, the holistic models predict a generally declining latency for letter detection, because the initial step in letter detection (i.e., word-level encoding) will be occurring more rapidly. The race models, on the other hand, predict that with increasing word frequency there will be an increasing chance that the word-level encoding will win the encoding race, resulting in an increase in the latency for letter detection (i.e., the word code will conceal the letter codes). Two experiments are reported, and the obtained pattern of latency data appears to be most consistent with the race models.

O6-methylguanine-DNA methyltransferase activity in tissues and cells of the rat respiratory tract

A product of alkylating agents and DNA, O6-methylguanine (O6-MG), can mispair with thymine, resulting in initiation of a carcinogenic tissue response. O6-alkylguanine-DNA alkyltransferase (AGT) is an acceptor protein responsible for repairing O6-MG. The purpose of our experiments was to characterize in vitro AGT activity in tissues and cells in the respiratory tract, a target tissue for inhaled alkylating agents. Anatomically defined regions throughout the respiratory tract of male F344 rats were obtained. These included two regions of the lateral wall of the left and right nasal airway (maxilloturbinates and ethmoturbinates), trachea, extrapulmonary bronchi and peripheral lung. Alveolar type II cells were also used in these studies. Radioactive 3H-methylated DNA was synthesized for use in all experiments. Removal of [3H]methyl from O6-MG was measured by high-pressure liquid chromatography after incubation for up to 30 min of tissue and cell extracts with the [3H]DNA. With the exception of tracheal and bronchial extracts, all tissues and cells analyzed contained AGT activity, which was found to increase proportionally to the amount of protein added to reaction flasks. AGT activity in tracheal and bronchial extracts was only detected at the highest protein concentration used (1.5 mg protein/ml) and ranged from 10-15 fmol/mg protein. AGT activity was highest in the lung (integral of 75 fmol/mg protein) and a region of the nasal tissue, the ethmoturbinates (integral of 45 fmol/mg protein). AGT activity in the maxilloturbinates was about 50% less than the AGT activity measured in the ethmoturbinates. These data suggest that methylated DNA in specific regions of the rat respiratory tract should be readily repaired, albeit to different extents.

Transmission electron microscopy of small numbers of sorted cells

A new method that allows the transmission electron microscopic examination of as few as 1 x 10(4) cells obtained by flow cytometric sorting is described. The approach involves "sandwiching" fixed cells in an agarose case by a microcentrifugation system consisting of small-diameter cell-centrifugation tubes and subsequent processing of the cells by conventional techniques. The advantages offered by this method are discussed.

Radiobiology of ultrasoft X rays. I. Cultured hamster cells (V79)

Ultrasoft X rays (approximately less than keV) provide a useful probe for the study of the physical parameters associated with the induction of biological lesions because the spatial scale of their energy depositions is of nanometer dimensions, comparable to that of critical structures within the cell. We report on cell-killing experiments using cultured hamster cells (V79) exposed to carbon K (0.28 keV), aluminum K (1.5 keV), copper K (8.0 keV), and 250 kVp X rays, under oxic and hypoxic conditions, and as a function of cell-cycle phase. Our principal results are: RBE increases with decreasing X-ray energy; OER decreases with decreasing X-ray energy; and cell-cycle response is similar for all X-ray energies. Our RBE results confirm earlier observations using ultrasoft X rays on mammalian cells. The shapes of fitted curves through the data for each energy are statistically indistinguishable from one another, implying that the enhanced effectiveness is purely dose modifying. The results reported herein generally support the view that single-track effects of radiation are predominantly due to very local energy depositions on the nanometer scale, which are principally responsible for observed radiobiological effects.

Asbestos-induced changes in rat lung parenchyma

Fischer 344 rats have been exposed to UICC crocidolite by whole-body inhalation procedures for periods of 1 d to 12 mo. Material was obtained from the same location in the left lung, and the numbers of cells in the parenchyma were identified and determined by transmission electron microscopy. An immediate increase (1 d of exposure) was evident in the number of type II cells, suggesting a direct action of the dust on these cells. The number of interstitial and alveolar macrophages showed a significant increase after 3 mo of exposure. The number of alveolar macrophages containing dust particles after a 1-d exposure was 49%, and the corresponding value after 12 mo of exposure was 92%. The longer periods of exposure were associated with an increase in the number of particles per macrophage. Polymorphs appeared in the interstitium at airway bifurcations, prior to their appearance in the alveolar space. These bifurcations were also the initial sites where evidence of cell damage and collagen deposition was seen. In this experiment crocidolite appears to be weakly fibrogenic, and other factors may be needed to produce the marked lesions seen in human asbestosis.

Preparation of viable single cell suspensions of tracheal epithelial cells

This paper reports a procedure used for isolating the entire epithelial lining of the rat trachea. Isolated trachea was initially filled with 0.2% hyaluronidase and incubated at 37 degrees C for 30 min. Tracheas were flushed with medium and then reinflated with 0.5 microgram/ml cytochalasin B and re-incubated for 60 min. The tracheal lumens were again flushed and reinstilled with 24 iu/ml pronase and incubated for a further 30 min. The tracheas were flushed again and the cells removed enumerated and viability assessed by trypan blue dye exclusion. Cell yields (X 10(6)) from 30 consecutive Fischer 344 rats were 5.06 +/- 0.16 (s.e.m.) and the mean percentage of viable cells was 83.13 +/- 1.10 (s.e.m.). This cell yield was close to the estimated tracheal cell population (5.3 X 10(6)). The suspensions were predominantly single cells which apparently retained a normal ultrastructural appearance.

Silica-induced alveolar cell tumors in rats

Min-U-Sil5, a form of alpha quartz, has been shown to induce peripheral lung tumors in rats exposed to the dust by inhalation. The animals were exposed to a nominal particle concentration of 12.4 mg/m3 for 8 hr/day, 4 days/week, for 2 years. The induced tumors were large and peripheral, and, when examined by electron microscopy, were found to be composed predominantly of alveolar type II cells. These cells were found in papillary, acinar, and solid forms of the tumors and were characterized by lamellar inclusion bodies. This is in contrast to the mouse, in which the papillary form was associated with Clara cells and the acinar form was linked with the type II cell. In this study, the Clara cell was a minor component of the tumor mass. No clear risk is established in man linking silica exposure to increased lung tumor rates.

Identification of inorganic dust particles in bronchoalveolar lavage macrophages by energy dispersive x-ray microanalysis

This study shows that energy dispersive x-ray microprobe analysis to identify and quantify intracellular particles in macrophages obtained by the minimally invasive method of bronchoalveolar lavage (BAL) can detect inorganic dust exposures of many different kinds. Bronchoalveolar lavage macrophages from 22 patients have been examined. Twelve patients had occupational exposure to asbestos, talc, silica, hard metal or printing ink, while 10 had no known history of dust exposure. X-ray microprobe analysis identified particles which related to the known exposures, superimposed on a background of other particles related to smoking (kaolinite and mica) or to the general environment (silicon, titanium, and iron). The particle identification provided useful objective confirmation of the known exposures, except for silica, which could not be distinguished from the general background levels. X-ray microanalysis using BAL macrophages can be helpful for clarification of mixed dust exposures, to identify particles when light microscopy indicates retained dust in patients with no known history of exposure, and to monitor retained particles after removal from exposure.

In vitro biological effects of volcanic ash from Mount Sakurajima

Mount Sakurajima in the south of the Kyushu Island of Japan erupts hundreds of times a year and continuously emits large amounts of ash. More than a million people live under this ash plume, and there is considerable concern about the possible effects of this on their health. We have studied the physicochemical characteristics and in vitro effects of airborne ash collected at 8 km from the crater. More than 30% of the ash was found to be SiO2 (w/w) with most of the particles within the respirable size range. The ash did not inhibit the colony formation of V79-4 cells and failed to activate complement or generate chemotactic factor activity in samples of fresh human serum. It was minimally active in causing the release of lysosomal enzymes from human neutrophile, and did not cause arachidonic acid release from macrophage-like cells. These results were in accord with our epidemiological study, in which very low prevalences of nonspecific respiratory disease were demonstrated even at the area with highest ash exposure.

The cytotoxicity of kaolin towards macrophages in vitro

The inhalation of china clay dust by man can cause pneumoconiosis. In an attempt to identify the factors responsible the cytotoxicity in vitro of china clay dust towards mouse peritoneal macrophages was examined. Respirable dusts collected at china clay drying plants were cytotoxic towards the cells. This activity was caused by kaolinite (the major mineral in china clay) and was not due to the presence of ancillary minerals. The cytotoxicity of kaolinite was not due to particle morphology and the positively charged edges of the mineral contributed only slightly to cytotoxicity. An electron microscope study showed that macrophages phagocytosed PVPNO-coated kaolinite particles indicating that the low cytotoxicity of these particles was not due to poor phagocytosis. Residence of china clay in rat lungs appeared to reduce its cytotoxicity. It was concluded that the cytotoxicity of kaolinite was probably related to the proposed amorphous silica-rich gel coating on the particles. The relevance of the findings in vitro to the effects in vivo of china clay is discussed.

Primary angiosarcoma of the mediastinum: light and electron microscopic demonstration of Factor VIII-related antigen in neoplastic cells

An angiosarcoma developed in the superior mediastinum of a 50-year-old white woman. The ultrastructural appearance and the significance of Factor VIII-related antigen within the neoplastic cells are discussed.

Pluripotential nature of mesotheliomata induced by inhalation of erionite in rats

Mesotheliomata can be induced more rapidly and more frequently by inhalation of erionite than by asbestos inhalation. Erionite-induced tumours have in general a similar ultrastructural appearance to inoculum-induced pleural and peritoneal mesotheliomata. Unusual features of these tumours were the presence of dense-cored vesicles and cells staining positively for neuron-specific enolase which indicated the presence of endocrine cells. In addition, one tumour showed differentiation towards bone-forming cells. The expression of both epithelial and mesodermal characteristics demonstrates the pluripotential nature of mesothelial cells under certain circumstances.

Effect of asbestos on the P388D1 macrophagelike cell line: preliminary ultrastructural observations

The ultrastructural effects of mineral dusts on a macrophagelike cell line (P388D1) were studied by transmission electron microscopy. The cells were found to contain virus particles which probably did not exert a cytopathic effect toward the cells. During mitosis the asbestos fibers appeared to be pushed to the periphery of the cell. The distribution of the asbestos in the P388D1 cells was similar to that seen previously in cultured peritoneal macrophages, and it was concluded that the cytotoxic effect of asbestos towards the cells was due to mechanical effects, e.g., by penetrating structures such as the nucleus or phagosomes, by preventing the ordered movement of organelles with the cell or by disrupting the cytoskeletal framework of the cell.

Histology and ultrastructure of serially transplanted rat mesotheliomas

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The combined effects of light and acute ischemia on the structure of the rabbit retina: a light and electron microscopic study

The ultrastructure of the rabbit retina has been investigated to determine the combined effects of light and ischemia. Both eyes of 16 adult Dutch rabbits were exposed to light of an intensity known to be near or below the threshold for ultrastructural changes in the retina. In addition, one eye of each animal was subjected to one of four periods of pressure-induced total acute ischemia. Exposure to light alone resulted in only minor disturbances of the receptor cell outer segments. The remainder of the retina was of normal morphologic appearance. Exposure to the combined insults of light exposure and ischemia produced considerably more damage to the inner and outer retina. Light exposure combined with short periods of ischemia (15 to 30 min) resulted in edema of the pigment epithelium and disturbances of the receptor cell inner and outer segments. Light exposure combined with longer ischemic periods (45 to 60 min) resulted in severe disturbances in the structure of the pigment epithelium, breakdown of the receptor cell outer segments, rupture of the inner segment mitochondria, and severe edema of the neural retina. The implication of this addictive or synergistic action of light and ischemia is discussed.

Prednisolone binding to albumin and transcortin in the presence of cortisol

The protein binding of prednisolone was assessed in a 5% albumin solution and in pooled human serum, alone and in the presence of various amounts of cortisol. Significant displacement of prednisolone from transcortin binding sites occurred with little or no change in transcortin binding capacity or affinity constant for prednisolone, suggesting competitive inhibition of prednisolone binding by cortisol. Little or no displacement of prednisolone from the protein binding sites on albumin occurred though a decrease in the number of binding sites (four vs two), and an increase in the affinity constant for the albumin-prednisolone interaction (4.32 X 10(2) vs 9.43 X 10(2) M-1) occurred in the presence of cortisol. Allosteric conformational changes may occur in albumin structure in the presence of cortisol. These alterations have no effect on the fraction of prednisolone bound to albumin.

Neuron specific enolase (NSE) immunostaining detection of endocrine cell hyperplasia in adult rats exposed to asbestos

Hyperplasia of endocrine cells in the lung of the adult rat exposed to asbestos has only been characterised so far by electron microscopy as there is a lack of reliable staining techniques for their demonstration at light microscopical level. Neuron specific enolase (NSE), an isoenzyme of the glycolytic enzyme enolase has recently been shown to be present in lung endocrine cells. In this study we reveal a marked endocrine cell hyperplasia at light microscopical level in the lungs of adult rats exposed to asbestos using antibodies to NSE. Very large groups of NSE-immunoreactive cells (20-80) were only observed in the lungs of rats exposed to asbestos for 12 months. In addition smaller groups of cells (2-10) known to be present normally and to decrease with age, were rarely noted in the controls but were frequently detected in the treated rats. Immunoreactive NSE is therefore a very good marker for endocrine cell hyperplasia and thus of early neoplastic changes.

An ultrastructural study of the effects of asbestos fibres on cultured peritoneal macrophages

The effects of crocidolite and chrysotile fibres on lavaged peritoneal macrophages have been studied by both scanning (SEM) and transmission (TEM) electron microscopy. SEM provided little information (as the surface topography did not reflect the underlying cytoplasmic organization) except that it showed that individual macrophages often partially engulfed many long fibres in a random fashion. TEM revealed the fibres in and protruding from membrane-bound vacuoles, free in the cytoplasm and penetrating the nucleus. The cellular distribution of the fibres is discussed in terms of the cytotoxic nature of the fibres and their ability to produce a selective release of enzymes from the macrophages.

Preliminary observations of the effect of inhalation of PVC in man and experimental animals

Attention has been focussed, both in man and experimental animals, on the effects of inhalation of the gas monomer, vinyl chloride. Recently, note is being taken of the possible effects of the inhalation of the polymer in man. The particles in question are those produced commercially as paste polymer or dispersion polymer or having an average diameter of 0.15 micrometers, and accounting for more than 10% of the production in Britain. There are now strict regulations for the control of the monomer gas, but the particles are regarded as nuisance dust and their emission is not covered by specific legislation. Our studies on rats, where both inhalation and implantation methods of exposure have been used, and examination of tissue from human cases exposed to paste polymers, indicate that these small particles can only be regarded as evidence of exposure, and on present evidence there is no indication of causation of significant pulmonary disease. Techniques have been developed by which these particles can be demonstrated in ordinary histological preparations and by transmission electron microscopy.

The permeability of the posterior blood ocular barrier after xenon photocoagulation: a study using fluorescein labelled dextrans

Xenon photocoagulation burns in the rabbit fundus were studied angiographically with fluorescein labelled dextrans of molecular weights in the range 3000 to 150 000. Recent photocoagulation burns showed dye leakage to all molecular weights used. Angiograms 2 days after burns had been produced showed leakage of dextrans of molecular weights up to and including 70 000 but no leakage of dextran of 150 000 molecular weight. At 7 days after photocoagulation healed burns remained permeable to dextrans of molecular weight 3000 or 20 000, but in the majority of eyes such burns did not leak dextrans of over 40 000 molecular weight. The clinical significance of the selective nature of photocoagulative damage to the posterior blood ocular barrier is discussed.

Sectioning and imaging hard mineral fibres in biological tissues

A technique is described which overcomes the problems associated with sectioning biological tissue containing hard mineral fibres. 0.2--0.5 micrometer thick sections were cut with a diamond knife, placed in a folding grid, conventionally stained with uranyl acetate and lead citrate and viewed at an accelerating voltage of 200 kV in the scanning transmission mode.

The post-mortem vacuoles of Schlemm's canal

A two-part study was conducted in which post-mortem changes were investigated in the baboon outflow system. It was found that the meshwork cells closest to the chamber angle were particularly susceptible to post-mortem advance. Post-mortem vacuoles developed in the endothelium of Schlemm's canal and by light microscopy these structures could be mistaken for giant vacuoles. On the other hand it was shown by electron microscopy that the giant vacuoles which have been implicated in the transendothelial transfer of aqueous humour and post-mortem vacuoles were distinct and separate entities.

Serum protein binding of prednisolone in four species

The protein binding of prednisolone in serum from humans, rabbits, dogs, and rats was determined by equilibrium dialysis. Two nonlinear least-squares regression programs were used to characterize transcortin and albumin binding of the steroid. The animal species differed markedly in their ability to bind prednisolone, but the rabbit was most similar to humans in transcortin concentration and affinity constant.

Release of lamellar bodies from alveolar type 2 cells

The release of lamellar bodies from rat alveolar type 2 cells has been studied during a 12hr dark/12hr light cycle. A proportion of the type 2 cell population was ultrastructurally abnormal. The cellular changes formed a spectrum raninging from mild to severe, culminating in rupture of the cell and release of its contents into the alveolar air space. The majority of aberrant cells were observed in animals killed during the dark period. A holocrine secretory mechanism is suggested for the release of lamellar bodies containing the surface active phospholipids of the alveolar lining. The release of lamellar material by a process of exocytosis was also observed, but only rarely, in spite of the numerous lamellar bodies seen in each cell cross-section.

Vitreo-scleral fluid transfer in the rabbit

Experiments were carried out to see whether a radioactive tracer placed in the vitreous of a rabbit eye could be detected on the sclera. A solution of Xenon-133 dissolved in saline was injected into the vitreous of six rabbits and collecting tubes containing activated charcoal were placed on the sclera. The presence of Xenon in these tubes confirmed that vitreoscleral transfer had occurred. It was calculated that on average, 2% of the Xenon had appeared over the whole sclera. A mathematical analysis of the shape of the activity curve of the tracer on the sclera revealed that its appearance was probably due to diffusion across the outer layers of the eye.