Cellulose Digestion by the Silverfish Ctenolepisma Lineata*

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Abstract
1. The silverfish, Ctenolepisma lineata, on a diet of cellulose alone shows a respiratory quotient of close to unity, indicating utilization of carbohydrate, presumably derived from cellulose. 2. The silverfish may gain weight temporarily on a diet of cellulose alone although the diet is not satisfactory for prolonged feeding. 3. The silverfish digests part of the cellulose ingested, the utilization efficiency being comparable to that of the dairy cow. 4. Silverfish fed cellulose uniformly marked with 14C respire 14CO2, indicating that cellulose is metabolized and therefore must have been digested. 5. The gut of the silverfish contains many micro-organisms, but none of the bacteria grown in favourable culture media are capable of digesting cellulose. A few moulds do, but they are never seen growing in the gut and are presumably developed from spores grazed from wood by the silverfish. 6. Bacteria-free silverfish were obtained by washing eggs in a solution of mercuric chloride and ethanol and raising the nymphs on rolled oats and vitamins under aseptic conditions. 7. Bacteria-free silverfish fed cellulose uniformly marked with 14C respire 14CO2, indicating that even in the absence of micro-organisms, C. lineata metabolizes cellulose and therefore must have digested it. 8. A cellulase was demonstrated in extracts of the midgut. A cellobiase and an amylase were also shown to be present. The pH optima for the cellulase are 4.0 and 6.0, with a smaller peak occasionally showing at 7.7. For cellobiase the optima were 4.5 and 6.5. 9. The cellulase was isolated in the 60 and 70% ammonium sulphate saturated fractions of the soluble proteins from the midgut.