Gibson et al.1 have proposed that mucus normally inhibits passive flow of water and small ions, but fails to perform this function adequately in patients with cystic fibrosis (CF), due to excessive secretion of calcium for exocrine glands. Negus2 first suggested, without adequate experimental data, that epithelial mucins control water and electrolyte permeability. For reasons discussed here, this concept, and other facets of the Gibson hypothesis, are not supported by Gibson's investigations.

The authors developed an assay (Exp. I) for movement of water through films of submaxillary saliva (SMS) layered on dialysis membranes. When movement through CF and control films was compared, disparate relationships between film thickness and water permeability were observed.

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