1. Ciliary activity is significantly influenced by chemical and physical properties of the liquid medium in which the cilia beat. 2. We studied the effect of changes in pH, ionic strength and viscosity on the ciliary beat frequency (CBF) of explants of human respiratory mucosa. 3. Optimal CBF was elicited at pH 7 . 0-9 . 0, with a marked reduction of CBF outside these limits. The CBF was well preserved at NaCl concentrations between 5 g/l (80 mmol/l) and 12 g/l (200 mmol/l), but there was rapid loss at concentrations below 0 . 5 g/l (10 mmol/l). The cilia beat best at viscosities below 1 . 0 centipoises (1 mN s m-2). Increase of the viscosity gradually decreases CBF with a significant drop at viscosities above 87 millipoises. 4. It is concluded that the above limits may fairly accurately indicate the actual physical characteristics of the periciliary environment ('sol layer') in vivo.

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Twenty-eight sputum samples collected from 20 patients with chronic bronchial asthma of atopic and intrinsic clinical types were incubated with human bronchial explants to study their influence on ciliary motility. Of these, 19 (68%) of the sputa exerted a ciliary inhibitory effect of varying degree in a two-hour period. Analysis of the data indicates that (1) the ciliary inhibitory effect was invariably present when patients produced a distinctive slurry sputum; (2) this occurred more frequently during clinical exacerbations; (3) the induced ciliary inhibition was reversible on removal of the sputum; (4) the intensity of the ciliary inhibitory effect decreased with clinical improvement of the patient; (5) the inhibitory effect was unrelated to the medications used; (6) it was equally common in the atopic and the intrinsic types of asthmatic patients; (7) the effect was not pH dependent or related to the degree of eosinophilia. The ciliary inhibitory factor in sputum was identified as having a molecular weight of 6000-8000. It may play a part in the pathogenesis of asthma and recognition of sputum containing it carries implications for treatment.