Abstract
MAINLY because of the observed inhibitory effects of sulphonamides on egg shell formation1–3 and partly because the enzyme carbonic anhydrase is present in the reproductive tract of the laying hen4, it has been generally assumed that this enzyme plays an important part in eggshell formation by making available the carbonate ion. Nevertheless, while some workers4,5 have attempted to correlate egg-shell formation with increased carbonic anhydrase activity of the uterine tissue of laying hens, little attention has been focused on the role the shell membrane might play during shell deposition. The keratin-like shell membranes6 which enclose the egg-white are believed to be attached to the major part of the shell by a mammillary layer, so called because of the presence of numerous aggregates (the mammillae) of a substance with the staining characteristics of a mucoprotein7.
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