Document KJdE8V3NoL7DQZgBGw4G4zejX

;l ! of the French, and for. description, but we don't regard thes categories as haring any great significance,' Natural his tory, and the prognosis and everything else, of ina pinhead, micro-nodular and nodular is similar. Then, we come .to progressive fibrosis. A, 5, C and D, depending on the size of the shadows, and eventually, D, which you can't see on the table there which has distor tion. Well, now, that is the.classification, and now I want to say one or two words to try and persuade you that it may be quite a good one. First of all, it is a purely radiological classification. It is used by looking at the radiograph and without any further information at all,wr.ich. is what 'a radiological classification should be. Secondly, the categories are based on studies of the-progression of the disease, so that the earlier cate gories represent earlier stages in the natural development of the disease, than do the later categories. Thirdly, in justification of our categories of . simple pneumoconiosis, we have found evidence which I shall, show in my next talk on the epidemiological side, evidence that there is a fairly direct quantitative relatlonsnip between the amount of dust exposure required to produce tr.9S three categories. The ratio of dust exposure required co produce Category Two is about twice that required co croruce SEVENTH SARANAC -0195