Effects of different vegetable dust exposures

Valić, F., and Žuškin, E. (1972).Brit. J. industr. Med.,29, 293-297. Effects of different vegetable dust exposures. In order to establish the rank of biological activity of vegetable dusts, five groups of non-smoking female workers exposed to similar concentrations of hemp, flax, cotton, sisal, and jute airborne dust, respectively, were compared as to the prevalence of byssinosis, chronic respiratory symptoms, and one-second expiratory volume changes over the Monday shift. The groups were selected in such a way as to differ in the distribution of age and length of exposure to the respective dust as little as possible.

The prevalence of byssinosis in hemp and flax workers was approximately equal (44% and 43% respectively), in cotton workers it was considerably lower (27%), while no byssinosis was caused by either sisal or jute dust. The highest prevalence of other chronic respiratory symptoms was recorded in hemp workers (39%), followed by flax (36%) and cotton workers (27%), while in sisal (13%) and jute workers (13%) it was the lowest.

Significant mean FEV_1·0 reductions over the shift were recorded in all the groups of textile workers with the largest reductions in hemp workers (19%) followed by flax (11%), cotton (8%), sisal (7%), and jute workers (5%). The application of orciprenaline before the shift diminished the mean acute FEV_1·0 falls over the work shift in all the groups studied.

     

Respiratory response in simultaneous exposure to flax and hemp dust

Žuškin, E., and Valíc, F. (1973).British Journal of Industrial Medicine,30, 375-380. Respiratory response in simultaneous exposure to flax and hemp dust. The effect of exposure to high concentrations of mixtures of hemp and flax dust was studied in 124 workers in two textile mills (mill A: 65-70% hemp and the rest flax, mean dust concentration 13·9 mg/m³; and mill B: about 35% hemp and the rest flax, mean dust concentration 15·8 mg/m³). A high prevalence of byssinosis was found in both mills (80% in mill B; 46·8% in mill A) after a mean exposure of no more than 13 years. In both mills, byssinotics had a higher prevalence of all chronic respiratory symptoms than non-byssinotics. This difference was more pronounced in mill A. Forty-eight percent of byssinotic women and 43% of byssinotic men had byssinosis of grade 2 or 3. Significant mean acute reductions in FEV_1·0 and ˙V_max 50% VC on Monday were recorded in subjects with and without byssinosis with a significantly larger mean reduction in byssinotics (FEV_1·0, P < 0·01; ˙V_max 50% VC, P < 0·05). ˙V_max 50% VC proved to be a more sensitive test for detecting acute effects of vegetable dust than FEV_1·0. The acute respiratory response of the subjects exposed to similar concentrations of flax and mixtures of two different proportions of flax and hemp dust was found to be equal.     

A comparative study of respiratory function in female non-smoking cotton and jute workers

Valić, F., and Žuškin, E. (1971).Brit. J. industr. Med.,28, 364-368. A comparative study of respiratory function in female non-smoking cotton and jute workers. To compare the effect of cotton and jute dust, respiratory symptoms were studied and respiratory function measured in 60 cotton and 91 jute non-smoking female workers of similar age distribution, similar length of exposure to dust, and exposed to similar respirable airborne dust concentrations. Cotton workers had a significantly higher prevalence of byssinosis, of persistent cough, and of dyspnoea (P < 0·01) than jute workers. Among cotton workers 28·3% were found to have characteristic symptoms of byssinosis, whereas none was found among jute workers.

Exposure to cotton but also to jute dust caused significant reductions of FEV_1·0, FVC, and PEF (P < 0·01) over the first working shift in the week. Functional grading of jute and cotton dust effects has shown that about 30% of cotton workers had functional grades F1 and F2, while only 13% of jute workers were found in the same grades (F1). It is concluded that cotton dust may be considered more active than jute though the latter cannot be considered inactive.

     

Some Pharmacological Actions of Cotton Dust and Other Vegetable Dusts

Aqueous extracts of cotton and other vegetable dusts cause contraction of the isolated ileum and tracheal muscle of the guinea-pig, and of isolated human bronchial muscle. The levels of this contractor activity place the dusts of cotton, flax, and jute in the order of the probable incidence of byssinosis occurring in the mills spinning these fibres.

Extracts of cotton dust possess a histamine-liberating activity and contain a permeability-increasing component. These actions are of plant origin and are found in the pericarp and bracts of the cotton boll. Histamine and 5-hydroxytryptamine have also been found in some cotton dust samples. The formation of histamine by bacterial action in cotton dust does not take place under conditions found in cotton mills. The smooth muscle contractor substance is organic in nature, relatively heat-stable, and dialysable. The relevance of these results to the symptoms of byssinosis is discussed.

     

Effects in man and rabbits of inhalation of cotton dust or extracts and purified endotoxins

Cavagna, G., Foá V., and Vigliani, E. C. (1969).Brit. J. industr. Med.,26, 314-321. Effects in man and rabbits of inhalation of cotton dust or extracts and purified endotoxins. The incidence of byssinosis in workers in a cotton card-room, where the airborne concentration of bacterial endotoxins was 7·2 μg./m.³, was 32%; and 47% in a hemp card-room where the endotoxin concentration was 8·7 μg./m.³; no cases were observed among workers exposed to only traces of endotoxins.

The effect of the inhalation by aerosol of purified Escherichia coli endotoxin on F.E.V._1·0 and F.V.C. was studied in normal subjects and in patients with chronic bronchitis. A significant reduction in F.E.V._1·0 lasting more than 6 hours was observed in two out of eight normal subjects, in one out of three subjects with chronic bronchitis inhaling 80 μg. endotoxin, and in one out of four subjects with chronic bronchitis inhaling 40 μg. endotoxin. These results show that the inhalation of bacterial endotoxin can produce, in some individuals, changes in F.E.V._1·0 similar to those experienced on Mondays by some card-room workers.

A study of the mechanism of pathogenesis of inhaled bacterial endotoxins was carried out on rabbits subjected for 20 weeks to aerosols of purified E. coli endotoxin (20 μg./day) and cotton extract (2 mg./day). This treatment produced patterns of bronchitis: i.e., a increase in the respiratory tract fluid with increased protein content and characteristic histopathological changes. The bronchitis occurred after the appearance of cross-reacting circulating antibodies against E. coli endotoxin and cotton extract. These antibodies were detected with the haemagglutination tests after the first three weeks of treatment, and in subsequent weeks reached progressively higher titres, up to a maximum of 1:512.

A challenging aerosol of 0·1 mg. E. coli endotoxin in two rabbits and 10 mg. cotton extract in another two of the rabbits treated as above produced a marked increase in pulmonary resistance lasting more than two hours. In control rabbits a challenging aerosol of 1 mg. endotoxin or 100 mg. cotton extract caused only a moderate increase in pulmonary resistance, which returned to normal in less than one hour.

It may be concluded that the repeated inhalation of endotoxins induces in rabbits a state of hypersensitivity and at the same time the appearance of inflammatory reactions in the bronchi and alterations in the mechanical properties of the lung. These changes may be significant in the pathogenesis of byssinosis.

     

A study of rope workers exposed to hemp and flax

Smith, G. F., Coles, G. V., Schilling, R. S. F., and Walford, Joan (1969).Brit. J. industr. Med.,26, 109-114. A study of rope workers exposed to hemp and flax. Respiratory symptoms and ventilatory capacities were studied in 54 men and 22 women exposed to the mixed dusts of hemp and flax in an English rope factory. The preparers and most of the spinners were exposed on average to concentrations of 1·7 mg./m.³ total dust and 0·5 mg./m.³ fine dust. Those employed on subsequent processes had lower exposures at concentrations of 0·5 mg./m.³ total dust and 0·1 mg./m.³ fine dust.

Six men, all in the high exposure group, had symptoms of byssinosis. After adjustment for age and standing height there was no statistically significant difference in the forced expiratory volume (F.E.V._1·0) between those in high dust concentrations and those in low concentrations; neither was there a significant difference between the ventilatory capacities of men with and without byssinosis.

This study shows that byssinosis is an occupational hazard confined to male workers in this factory. It does not appear to be a very serious problem and will diminish with the increasing use of synthetic materials instead of natural fibres.

     

Differential Aerosol Challenge Studies in Byssinosis

Cotton textile mill workers with conditions diagnosed as byssinosis or not byssinosis by a modified Medical Research Council (MRC) questionnaire were challenged with extracts of cotton dust fractionated by filter membrane dialysis, and volatilization. Byssinotic subjects responded with a significant decrease in FEV_1.0 and with clinical symptoms to the inhalation of whole raw cotton extract and nonvolatile, nondialyzable cotton extract compared to saline, volatile extract, and dialyzable extract. Subjects without byssinosis responded the same to saline as to all other extracts. Comparison of responses of byssinotic and nonbyssinotic subjects showed no statistically significant differences with any extract. It was concluded that the active agent in cotton dust is water soluble, filterable at 0.22μ, nonvolatile at 40C, and nondialyzable but may not be active only in that group of patients identified as byssinotic by questionnaire.     

Respiratory symptoms and cotton dust exposure; results of a 15 year follow up observation

Aims: To determine chronic effects of long term exposure to cotton dust and endotoxin on incidence of respiratory symptoms and the effect of cessation of exposure.

Methods: Respiratory health in 429 Chinese cotton textile workers (study group) and 449 silk textile workers (control group) was followed prospectively from 1981 to 1996. Byssinosis, chest tightness, and non-specific respiratory symptoms were assessed by means of identical standardised questionnaires at four time points. Exposures to cotton dust and endotoxin were estimated using area samples collected at each survey. Incidence and persistence of symptoms were examined in relation to cumulative exposure and exposure cessation using generalised estimating equations (GEE).

Results: Among cotton workers, the cumulative incidence of byssinosis and chest tightness was 24% and 23%, respectively, and was significantly more common in smokers than in non-smokers. A high proportion of symptoms was found to be intermittent, rather than persistent. Among silk workers, no typical byssinosis was identified; the incidence of chest tightness was 10%. Chronic bronchitis, cough, and dyspnoea were more common and persistent in the cotton group than in the silk group. Significantly lower odds ratios for symptoms were observed in cotton workers who left the cotton mills; risk was also related to years since last worked. Multivariate analysis indicated a trend for higher cumulative exposure to endotoxin in relation to a higher risk for byssinosis.

Conclusion: Chronic exposure to cotton dust is related to both work specific and non-specific respiratory symptoms. Byssinosis is more strongly associated with exposure to endotoxin than to dust. Cessation of exposure may improve the respiratory health of cotton textile workers; the improvement appears to increase with time since last exposure.

     

Dust Diseases in Dundee Textile Workers: An Investigation into Chronic Respiratory Disease in Jute and Flax Industries

A survey of respiratory symptoms and function was carried out in Dundee among 123 men and women in the jute industry and 242 in the flax industry. The selection of workers was biassed in favour of those working in the dustier departments as judged by eye and those in the older age groups. A group of 72 men in a heavy engineering firm were also selected as controls for comparison.

Chronic bronchitis, as defined by Ogilvie and Newell (1957) was recorded in 27% of those interviewed, whose average age was 49. Byssinosis of various grades was recorded in 30% of all working in flax; of these 35 had cough alone worse on Monday, 34 had other respiratory symptoms worse on Monday and in only four persons did the exacerbation persist longer in the week.

In spite of the occurrence of byssinosis, chronic bronchitis was no more prevalent among flax workers than among the others, the average ventilatory function was no worse, and radiographs of the chest revealed no differences. The characteristic fall in expiratory flow rate during the course of exposure to flax dust on Mondays is similar to that found in cotton workers, and is absent in jute workers and in flax workers not admitting to symptoms of byssinosis.

     

Studies on the aetiology of byssinosis

Taylor, G., Massoud, A. A. E., and Lucas, F. (1971).Brit. J. industr. Med.,28, 143-151. Studies on the aetiology of byssinosis. A condensed polyphenol based on leucocyanidin has been extracted from the cotton plant. The reaction between this material and human serum has been demonstrated using both a precipitin and a passive agglutination technique. Sera from 196 cardroom workers not suffering from byssinosis, 177 byssinotic cardroom workers, and 203 controls were tested for reactivity with the condensed polyphenol using the passive agglutination technique. Significant differences in mean titres were obtained between cardroom workers and controls and between byssinotic and non-byssinotic cardroom workers. It was shown that while the mean titre in non-byssinotic cardroom workers remains relatively constant with respect to duration of employment, the titre in those cardroom workers suffering from byssinosis shows a progressive rise with duration of cardroom exposure.

Inhalation of solutions of the condensed polyphenol by normal control subjects and by non-byssinotic cardroom workers produced neither symptoms nor changes in FEV_1·0 or FVC. On the other hand, inhalation of the material by byssinotic cardroom workers induced symptoms identical with those experienced on exposure in the cardroom on Mondays. Because of the subjective nature of byssinosis, this inhalational study was repeated as a double-blind trial which completely confirmed the above observations.

     

Peak flow rate in relation to forced expiratory volume in hemp workers

Žuškin, E., and Valić, F. (1971).Brit. J. industr. Med.,28, 159-163. Peak flow rate in relation to forced expiratory volume in hemp workers. Measurements of the forced expiratory volume in one second (FEV_1·0) and the peak expiratory flow rate (PEF) were made in 99 non-smoking female hemp workers before and after the shift. A significant mean reduction of both FEV_1·0 and PEF (P<0·01) over the shift was found in workers both with and without byssinosis but the relative reductions of PEF were more pronounced (FEV_1·0 15·3%; PEF 20·8%). There was a significant positive correlation (P<0·01) both between absolute FEV_1·0 and PEF values measured before work (with byssinosis r = 0·605; without byssinosis r = 0·461), and between FEV_1·0 and PEF changes over the shift (with byssinosis r = 0·725; without byssinosis r = 0·631). There was also a significant correlation between FEV_1·0 and PEF changes following Alupent inhalation after the shift with more pronounced effects on PEF. The coefficients of variation in FEV_1·0 and PEF measurements (by the Bernstein type spirometer and the Wright peak flow meter) proved approximately equal.     

Immunological findings in hemp workers.

Immunological status and its relation to respiratory findings were studied in 42 female textile workers occupationally exposed to hemp dust and in 49 female control workers. Skin prick tests with hemp or flax dust extracts from different parts of the mill in hemp workers demonstrated the following frequencies of positive tests to antigens: a mixture of hemp and flax extracts (64%), followed by flax extracts (48%), hemp from combing machines (41%), hemp from carding machines (38%), hemp from spinning and weaving machines (33%), and hemp from softening machines (20%). The prevalence of positive skin tests to hemp or flax allergens in control workers was consistently lower, ranging from 21 to 5%. Increased total serum IgE was recorded in 35.7% of hemp workers compared to only 5.0% of control workers (P < 0.05). Hemp workers with positive skin tests had significantly higher prevalences of chronic respiratory symptoms than those with negative skin tests. There were, however, no differences for acute symptoms between workers with positive and negative skin tests. Across-shift changes and baseline lung function were not different when compared by immunologic status. We showed additionally that a water-soluble extract of hemp dust causes a dose-related contraction of nonsensitized guinea pig tracheal smooth muscle when studied in vitro. Our results suggest that frequent immunologic abnormalities can be documented in hemp workers but, with the exception of chronic respiratory symptoms, in general, these do not correlate with respiratory findings.     

VENTILATORY CAPACITY CHANGES ON EXPOSURE TO COTTON DUST AND THEIR RELEVANCE TO BYSSINOSIS IN AUSTRALIA

The same plan of investigation as was used in a previous study of jute workers (Gandevia and Milne, 1965) has been applied to a survey of 50 workers in the blowroom and carding and spinning area of a Sydney cotton mill. Significant decreases in ventilatory capacity were recorded on Friday, Monday, and the following Thursday, with, on the average, complete `overnight' recovery, as indicated by similar morning values. Slightly, but not significantly, greater differences were observed in seven subjects with mild byssinotic symptoms and in five subjects with an observed productive cough on request. No effect of sex, shift, or history of cough and sputum was demonstrable. By contrast with the jute workers, no influence of smoking habit was apparent. The larger decreases in ventilatory capacity were observed in those with the higher F.E.V.<sub>1·0</sub>:F.V.C. ratios, whereas the reverse trend was noted in the jute workers. The occurrence of significant large decreases in those employed in the industry for less than a month, in conjunction with other evidence, suggests that a factor of `self-selection' may be operative among cotton employees in this country and may be related to the apparently low prevalence of clinically important byssinosis. Attention is drawn to two different patterns of change of ventilatory capacity over a week in subjects exposed to dusts sometimes associated with symptoms of byssinosis; the relationship of these changes and of chronic bronchitis to the development of clinical byssinosis is discussed.     

Byssinosis among jute mill workers

Although byssinosis in jute mill workers remains controversial, studies in a few jute mills in West-Bengal, India, revealed typical byssinotic syndrome associated with acute changes in FEV1 on the first working day after rest. The present study on 148 jute mill workers is reported to confirm the occurrence of byssinosis in jute mill workers. Work related respiratory symptoms; acute and chronic pulmonary function changes among exposed workers were studied on the basis of standard questionnaire and spirometric method along with dust level, particle mass size distributions and gram-negative bacterial endotoxins. The pulmonary function test (PFT) changes were defined as per the recommendation of World Health Organization and of Bouhys et al. Total dust in jute mill air were monitored by high volume sampling, technique (Staplex, USA), Andersen cascade impactor was used for particle size distribution and personal exposure level was determined by personal sampler (Casella, London). Endotoxin in airborne jute dust was analysed by Lymulus Amebocyte Lysate (LAL) "Gel Clot" technique. Batching is the dustiest process in the mill. Size distribution showed that about 70-80% dust in diameter of < 10 microm, 40-50%, < 5 microm and 10-20%, < 2 microm. Mean endotoxin levels found in hatching, spinning and weaving, and beaming were 2.319 microg/m3, 0.956 microg/ m3, 0.041 microg/m3 respectively and are comparable to the values obtained up to date in Indian cotton mills. Respiratory morbidity study reported typical byssinotic symptoms along with acute post shift FEV1 changes (31.8%) and chronic changes in FEV1 (43.2%) among exposed workers. The group with higher exposure showed significantly lower FVC, FEV1, PEFR and FEF25-75% values. The study confirmed the findings of the earlier studies and clearly indicated that the Indian jute mill workers are also suffering from byssinosis as observed in cotton, flask and hemp workers.     

A study of the acute and chronic changes in ventilatory capacity of workers in Lancashire cotton mills

Berry, G., McKerrow, C. B., Molyneux, M. K. B., Rossiter, C. E., and Tombleson, J. B. L. (1973).Brit. J. industr. Med.,30, 25-36. A study of the acute and chronic changes in ventilatory capacity of workers in Lancashire cotton mills. A prospective study of workers in 14 cotton and two man-made fibre spinning mills in Lancashire was carried out over a three-year period. A questionnaire on respiratory symptoms was completed at the start of the survey and again two years later. Up to six measurements of ventilatory capacity were made at six-monthly intervals. From these measurements the rate at which the forced expiratory volume (FEV₁) was declining (annual decline in FEV) was evaluated for 595 subjects. Six of the mills were visited on Mondays and in 199 operatives the ventilatory capacity was measured at both the beginning and end of the shift to evaluate its acute fall during work (Monday fall in FEV).

The mean annual decline in FEV for cotton workers was 54 ml/year and it was only 32 ml/year for workers in the man-made fibre mills but this lower value was attributable almost entirely to one of the two mills. For the jobs near the carding engines the annual decline was 22 ml/year higher than for speed-frame tenters. The annual decline for cigarette smokers was 19 ml/year greater than for non- and ex-smokers. The annual decline in FEV was not found to be related to symptoms of byssinosis or bronchitis, nor to present dust levels, bioactivity of the dust or air pollution, although the expected effect attributable to byssinosis turned out to be less than that which the survey was designed to detect.

The mean Monday fall in FEV was higher in cotton mills than in man-made fibre mills among those without symptoms of byssinosis and was correlated with present dust levels. For those with symptoms of byssinosis an increased Monday fall was found only in those processing coarse cotton.

For those subjects who completed the respiratory questionnaire on two occasions the chronic and acute changes in FEV were examined in relation to the change in symptoms of byssinosis. No association was found for annual decline in FEV but the Monday fall in FEV was greater for those who developed byssinosis during the survey than for those who remained free of symptoms, and was less for those who lost their symptoms than for those who retained them.

     

Byssinosis Prevalence and Flax Processing

Previous evidence suggested that byssinosis in flax workers is caused by the inhalation of dust of biologically retted flax. In the present study no cases of byssinosis were found among workers in a flax plant which produces yarn by chemical degumming instead of biological retting. The absence of byssinosis in this plant could not be attributed to differences in the quantities of dust developed as compared with the conventional retting procedure.

These findings support the view that the agent in flax dust which causes symptoms of byssinosis originates during biological retting of flax and is absent from unretted flax. Chemical degumming of flax appears to be superior to biological retting procedures with respect to the health of the workers.

     

Occupational allergy to <Emphasis Type="Italic">Limonium sinuatum</Emphasis> — a case report

Decorative flowers are known to be a cause of occupational allergy in the floral industry. The allergic manifestations induced by flowers include asthma, rhinoconjunctivitis and urticaria. We present a case of a 55-year-old woman, who has been working for the last 30 years as a gardener with various kinds of flowers, e.g., Limonium sinuatum (LS), chrysanthemum, sweet William (Dianthus barbatus) and Lilium. During the last 10 years she has developed nasal and eyes symptoms, dry cough, dyspnoea, chest tightness and wheezing. Clinical examination, routine laboratory testing, chest radiography, skin prick tests (SPT) involving common allergens, native plants pollens and leaves by the prick-prick technique, rest spirometry, methacholine challenge test and specific inhalation challenge test (SICT) were conducted. SPT results to common allergens were positive for grass pollens. SPT with native plants pollens and leaves showed a positive reaction only for LS. SICT induced an isolated early asthmatic reaction and significant increase in the number of eosinophils in the nasal lavage fluid. Additionally, significant increase in non-specific bronchial hyperreactivity was observed after SICT. To our knowledge, the presently described report is the first one of Limonium sinuatum induced occupational asthma and rhinitis in a Polish gardener.     

A comparative environmental and medical study of dust exposure in jute and cotton mills in Burma

Jute is extensively cultivated and processed in Burma, as well as "lower-grade" cotton. This study was conducted there to compare dust exposure in jute and cotton mills, to study the acute and chronic effects of dust exposure on workers, and to establish exposure-response relationship. A sample of 799 male and female workers in two jute mills and two cotton textile mills, as well as a control group of 153 matching subjects, was examined, and dust exposure in the work environment was evaluated. Very high dust concentrations existed in the early stages of jute processing and sorting, which were reduced when jute fibers got cleaner, as in drawing and spinning, and were related to the grade of the processed fiber. Much lower concentrations of dust existed in the cotton mills, but exceeded the TLV (ACGIH) only in opening and cleaning and in carding operations. However, byssinosis occurred only in workers exposed to cotton dust, particularly among males, and its prevalence was related to the level and duration of dust exposure. Chronic bronchitis, cough and wheezing occurred at higher rates among all workers than in the control, while irritation to nose and throat, eyes and skin prevailed only among jute workers. A significant reduction in FVC, FEV1.0 and PEF (before and during shift) was observed in workers compared to control subjects, and was related to workers' exposure and age; however, this reduction was not related to symptoms of different respiratory conditions. "Cheroots" smoking was found to be an important potentiating factor in the occurrence of non-specific respiratory diseases and reduction in FEV1.0, particularly among jute workers.     

Comparative study of the smooth muscle contractor activity of airborne dusts and of dustiness in cotton, flax, and jute mills.

A bioassay technique using isolated guinea-pig ileum was employed to compare the smooth muscle contractor activity of various dusts from mills in which the prevalence of byssinosis was known. The activity of dust from a mill spinning a coarse grade of cotton was several times greater than that in dust from a mill processing a fine grade of cotton. There was a similar order in the difference of the prevalence of byssinosis in these mills. However, the activities of fine cotton, flax, and jute dusts were very similar to each other, in spite of marked differences in the prevalence of byssinosis in these mills. For cotton dust, smooth muscle contractor activity was associated with all particle sizes, although the lowest level of activity was found in the largest sized fraction (less than 2 mm). Activity in the cotton dust extracts was not correlated with nitrogen, carbohydrate, or potassium content. However, about one-fifth of the activity of a cotton dust extract was associated with an insoluble particulate fraction. The possible chemical nature of the water-soluble contractor agent is discussed. It is concluded that, until the role of this agent in the pathogenesis of byssinosis has been established, the bioassay technique cannot be employed as a means of assessing the byssinogenic potential of cotton dust.     

Comparative study of the smooth muscle contractor activity of airborne dusts and of dustiness in cotton, flax, and jute mills.

A bioassay technique using isolated guinea-pig ileum was employed to compare the smooth muscle contractor activity of various dusts from mills in which the prevalence of byssinosis was known. The activity of dust from a mill spinning a coarse grade of cotton was several times greater than that in dust from a mill processing a fine grade of cotton. There was a similar order in the difference of the prevalence of byssinosis in these mills. However, the activities of fine cotton, flax, and jute dusts were very similar to each other, in spite of marked differences in the prevalence of byssinosis in these mills. For cotton dust, smooth muscle contractor activity was associated with all particle sizes, although the lowest level of activity was found in the largest sized fraction (less than 2 mm). Activity in the cotton dust extracts was not correlated with nitrogen, carbohydrate, or potassium content. However, about one-fifth of the activity of a cotton dust extract was associated with an insoluble particulate fraction. The possible chemical nature of the water-soluble contractor agent is discussed. It is concluded that, until the role of this agent in the pathogenesis of byssinosis has been established, the bioassay technique cannot be employed as a means of assessing the byssinogenic potential of cotton dust.