Research on the pathogenesis of chronic pulmonary diseases, particularly bronchitis and centrilobular emphysema, is hampered by a lack of testable hypotheses. There have been many observations, measurements correlations and multidiscipline studies of pati~ nts and thei~ pulmonary functions. More recently mechanical functions of human lungs in vitro have been studied. However, the yield in understanding the mechanisms of structural change has been meager so that the causes of loss of pulmonary function and of lung damage and destruction remain unknown. It is the purpose of this paper to organize information concerning clearance from alveoli and bronchioles into a hypothesis that will form the basis for the design of subsequent experiments. This will help determine priorities and permit the design of experiments that may be crucial in destroying or modifying the hypothesis.

This approach is recommended because facts accumulate much faster than they can be assimilated and organized to form a basis for cleclurtions, and because the concept tlwt lung disease results from the interaction of inhaled materials and the cells of the lung is too general for crucial testing. The disposal and fate of soluble particles or gases appear to depend upon solubility. This is another large subject nnd is outside the scope of this discussion. Hypotheses have been developed thn t would expbin the clearnnce of poorly soluble or in-