“…In workers previously uninfected a progressive primary lesion may develop from the initial infection, or the reinfection may follow so quickly upon the primary that a secondary lesion develops before the primary has had time to heal or acquired immunity to develop. Where working conditions are poor there is often an abnormal amount of dust, (Sutherland, 1940) for the period 1932-9. Of 1,397 deaths due to silicosis, active tuberculosis was present in 797 cases.…”