Most of ceramics manufacturing plants in Seto district are small in their scale. About 3, 000 workers working in such plants were examined, of which 60.6% were being exposed to dusts. Of these dust workers, 28.2% were found to be silicotic. The smaller the plant, the higher the morbidity of silicosis, e.g. in plants employing workers less than 50 in number, 32.2% of the worker were suffering from silicosis. The length of employment of these silicotic workers were mostly 15 to 25 years, and the size of granular shadows in the X-ray film were less than 3mm in most of them. These may be due to relatively low concentration of silica dusts in their working environment, as revealed by the present investigation. In those employed over 20 years, the density of granular shadows showed an increase in accordance with their length of employment. Values of ventilatory function tests of the lung, i.e. vital capacity, maximum breathing capacity, and timed vital capacity, showed decreases first in the medium degree of silicosis (as diagnosed by the X-ray) and was abnormally low in the high degree of silicosis. Most of both these cases showed disorders of expiratory ventilation, and the mixed type of ventilatory disorders was found in the rest. In the light degree of silicosis, there were a great many cases with almost nil ventilatory disorders. According to the progress of sicicosis, the compressibility of the lung decreased down to 0.100 l/cmH₂O and lower, while the viscous resistance increased up to about 4.00 cmH₂O/l/sec., thus increasing ventiratory work of the lung accompanied with impaired clinical pulmonary symptoms.

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