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All 607 men, aged 17 to 69, comprising a stratified sample of workers from one shipyard completed a respiratory questionnaire, clinical examination, and detailed spirometry. Chest radiographs were available on 332 men. Among the men aged 50-69 the prevalence of persistent cough and phlegm (chronic bronchitis) was 40%, of wheeze on most days 25%, and undue breathlessness on exertion 25%. After allowing for age the relative risk of welders and caulker/burners having these symptoms were respectively 2.8, 2.2, and 3.1 compared with other shipyard tradesmen. The effects were of comparable magnitude to and interacted with those of current smoking. Among the welders and caulker/burners who smoked, the relative risk of developing chronic bronchitis or undue breathlessness was related to the average fume exposure; the relative risk of wheeze was related to the average fume exposure in all smoking categories, with the strongest association in the ex-smokers. The occurrence of wheeze was also associated with a history of previous metal fume fever. A history of pleurisy but not of pneumonia was related to the fume exposure in the welders. After allowing for age and stature, forced expiratory volume (FEV1) was on average higher in young welders (age less than 30) than other tradesmen. In welders and caulker/burners who were current or ex-smokers, FEV1 and PEF were reduced in relation to the average fume exposure (mean reductions respectively 0.25 l and 0.99 l s-1). The FEV1% (of forced vital capacity), the flow rates at small lung volumes (MEF50%FVC and MEF25%FVC), the mean transit time, and its standard deviation were also reduced by fume exposure or the declines with age were increased, or both. No impairment was demonstrable in the non-smokers and many men had given up smoking with apparently beneficial results. The occupational component of the respiratory impairment related mainly to exposures in the past; information was needed on the effects of present conditions in the industry.

Two hundred and fifty men admitted to a thoracic surgical centre and matched controls were questioned in detail about their occupations after leaving school and their smoking habits. Of 201 men with confirmed bronchial carcinoma 58 gave a history of occupational exposure to asbestos, whereas only 29 out of 201 men matched for age and residential area who were admitted with other diseases gave such a history. This difference was statistically highly significant. The usual association of bronchial carcinoma with heavy smoking was observed, but asbestos exposure increased the risk of carcinoma whatever the level of smoking. These results are consistent with the hypothesis that asbestos exposure and the level of smoking act independently in causing bronchial carcinoma. The patients with carcinoma who had been exposed to asbestos presented on average three years earlier than those who had not been exposed. Asbestos regulations have eliminated the risk of exposure to workers in scheduled industries, so asbestos-induced diseases will probably be increasingly found among the many workers who have had incidental exposure to asbestos. It is therefore important to take a full occupational history.

Studies of lymphocyte sensitization in patients with asthma showed that the intrinsic and extrinsic forms of the disease fell into two distinct groups. Intrinsic disease showed a general sensitization to a number of non-specific antigens, while the extrinsic form had only slight elevation above normal values. These findings suggest that intrinsic asthma results from a defect of general immunity, whereas extrinsic asthma is a specific sensitization.

IN any study requiring the assessment of quantitative changes of a particular cell type in a suspension of mixed marrow elements, a method is essential whereby these cells may be counted with a known degree of accuracy. This problem was encountered in experiments designed to investigate the possible presence of a factor in pernicious anaemia serum affecting the rate of maturation of erythroblasts cultured in vitro, as reported by several workers (Rusznyak et al 1947, Lajtha 1950, Thompson 1950). Our results are presented elsewhere (Feinmann, Sharp and Wilkinson, 1952). In these experiments it was necessary to count absolute numbers of certain erythroblasts to a known degree of accuracy in order to determine whether observed differences in changes in their numbers on culture in different media were significant. The method of counting is described in detail since, with suitable modification, it has more general application. When it is not possible to count directly the number of cells in a known volume of fluid, the absolute number of a cell type per unit volume is derived by determining its proportion on smears and relating this to the total cell count. It is well known that in smears prepared on slides, the larger cells appear more frequently at the ends and edges of the smear than in the centre (Stephens et al 1920, Napier 1922, Gyllenswaird 1929, Boveri 1939, Dacie 1950). Methods of sampling of the slide, giving reasonably constant estimates of the proportion of a cell type on smears from one blood sample, have been devised (Dacie 1950). Our problem required the assessment of proportions of normal and megaloblastic erythroblasts in a marrow suspension, initially and after a period of incubation; during this incubation there might be not only a change in the relative propor