Reducing Activity and the Formation of Base in the Shore Crab, Carcinus Maenas

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Abstract
Crustacean cuticle consists essentially of chitin impregnated and coated with protein which is tanned with quinone (Dennell, 1947a). The outer surface is most heavily tanned, and the cuticle is further strengthened by calcification. The various theories as to the mechanism of calcification in crustacean and other biological material have been reviewed briefly by Digby (1967). Most appear unsatisfactory for various reasons, and evidence was outlined that calcification might arise from the formation of base by processes which are essentially electrochemical in origin. The quinone-tanned protein of the cuticle is electrically semiconducting and supports electrode action in suitable gradients of potential (Digby, 1965), and small potential differences may arise by diffusion or by active processes. Thus the deposition of calcareous salts might arise partly at least by action comparable to that which takes place at a metallic cathode. In support of this, the position of the initial calcareous deposits in Carcinus maenas (L.) was found to change with the gradient of sea-water salinity in the manner expected if some control were exercised by diffusion potentials, acting across a thin semiconducting layer to generate small changes of pH (Digby, 1968).

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