The object of this paper is to compare each of these two measurements of ventilatory capacity between preparers and non-preparers of flax in this industry.

Many factors, other than job, may influence ventilatory capacity; these include sex, smoking habits, the area of the mill, the type of fibre handled, byssinotic grade, age, and stem height. Within each sex and job, workers were divided into eight basic groups according to whether they did or did not smoke, whether the mill was in a town or rural area, and whether the mill processed only flax or flax plus synthetic fibres. Within each of these basic groups of non-byssinotic non-preparers, regression equations of the typeY = a + b₁X₁ + b₂X₂where Y = predicted F.E.V._1·0 or F.V.C. (litres), X₁ = age (years), X₂ = stem height (cm.), and a, b₁ and b₂ are constants derived from the data, were calculated for non-byssinotic non-preparers. These equations were used to predict the F.E.V._1·0 and F.V.C. of byssinotic and non-byssinotic preparers in each basic group, for each sex separately. The average predicted ventilatory capacity of preparers was then compared with the corresponding averaged observed ventilatory capacity.

It was found that (1) byssinotic flax preparers had a lower mean F.E.V._1·0 and F.V.C. than did comparable groups of non-byssinotic non-preparers, (2) non-byssinotic preparers had a lower average F.E.V._1·0 than did non-byssinotic non-preparers, (3) there is some evidence that preparers with symptoms of grade I or II byssinosis had a lower F.E.V._1·0 than did preparers with no, or only slight, symptoms of byssinosis (grades 0 and ½ respectively).