Pus, deoxyribonucleic acid, and sputum viscosity.

On 100 sputum specimens selected from patients suffering from chronic bronchitis, bronchiectasis, asthma, and cystic fibrosis total deoxyribonucleic acid (DNA) content has been related to macroscopic type, to total dry weight yield, and to the apparent viscosity of the secretion at 1350 s-1: since DNA may be present, either as fibres or within cells, in one-third of the specimens the contribution of each form to the apparent viscosity was assessed. The effect on sputum viscosity of the addition of DNA in vitro has also been studied. Whereas between mucoid, mucopurulent, and purulent macroscopic types a significant difference in total DNA and dry weight yield has been found, viscosity was not significantly correlated with purulence. Similarly, the concentration of either cells or fibres correlated significantly with total DNA but not with viscosity. The in vitro addition of DNA to sputum caused a significant increase in its viscosity, and reasons for the differences between the iv vivo and in vitro effect are discussed. Certain constituents of purulent sputum tend to increase viscosity and others to reduce it, and the influence of these varies in the several diseases studied.