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The requirements for sterols seem, therefore, to be qualitatively the same for the six insect species under investigation, but there are obvious quantitative differences. From a comparison of the growth on three diets relatively deficient in sterols (summarized in Table 2) it can be concluded that Sitodrepa, Ptinus and Ephe8tia kuehniella require larger quantities of sterols than Tribolium, La8ioderma and Silvanus. SUMMARY The sterol requirements of six different insect species have been investigated; all the insects require a sterol in the diet for growth. The quantitative requirements of sterols by different insects are different, but the qualitative requirements of the insects under investigation are the same. The specificity of the sterol requirements was studied. We gratefully acknowledge a Government grant from the Royal Society, which, partly, made this investigation possible. We are also much indebted to Prof.

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232 \vOKEs. OROAN. AND JACOBY-TEE ESTIMATION OF APPARENT VITAMIN-0 IR Foons [ffsmba, 1OUto be nttributed, ns Wokes.et ~1 1 . ~3 believe, to the lower pH of the processed mnterinl. Although it is much quicker to carry out nn annlysis with formnldehyde nt n pH of 3.5-5.0, this mny only be done if evidence has been obtnined tlint tlic mnterinl under exnmirntioii contnins no reductonc thnt condenses rnpidly with formaldehyde at this pH, nnd in doubtful cnscs it is snfer to use the reagent n t n pH of 2.0. Other dried foods which hnve been found to contain reductones or reductonc-like substnnces includc dried yenst extrncts and comniereinl prepnrntions of dcsiccnted soups.'It shodd, Iiowcwr, be cniphnaiscd tlint when vegetnbles are dried under conditions that nvoid cscessivc dnningc to the tissues, there are no significnnt nmountu of *interfering substnnces produced. Thrrs, the ascorbic acid vnluc of dried cnbbage, wlien carefully processed, nnd tt.hen freshly prepared, is identical whether determined by direct indophenol titrntion, or by biologicnl test (Allen et ~7 1 .~~1 lB), or by tlie forninldeliyde Inethod used here. DIscussro~It is hoped to cnrry out experiments, aith%iologicnl checks, of the efficiency of this formnldehyde method for estirnnting ascorbic acid iii n wide rnnge of processed foods. -In the rnenntinie, it seems ndvisoble, as fnr ns dehydrnted foods nre concerned, thnt nscorbic ncid vnlues should be detennined by n method cnpnble of differentinting between it nnd reductones nnd nllied substnnces. Finnlly, it should be stressed thnt the ascorbic acid content obtnined by this method with formaldehyde does not necessarily represent the true value, especinlly if hydroxytetronic acid is present. There is, however, no evidence thnt this acid occnrs in nnturnl products, though it might conceivnbly be produced in foods by certnin methods of processing. It hns beeii reported by Reichstcin and Oppe~inuer~~ that reductic ncid, closely related chemically to hydroxytetronic wid, is produced when xylose nnd other sugnr derivntives nre heated with strong minernl ncids. Wokes et al. hnve obtnined some evidence for its presence in some of their dried prepnrntions, nnd in the cnse of n dried cnrrot powder, mixed with dextrin and maltose, which they submitted to us, 36% of the dye-re,duciug substnnces present combined with formaldehyde rnpidly even n t pH 2.0. It seems probnblc thnt in this instance either hydroxytetronic or retuctie ncid or n siniilnr compound wns present. 111 doubtful cnses, the biological test still reinnins the finnl criterion. Nevertheless. the forinnldelivde nictliod docs offer a relntively titrntion with indophenol waa sufficient ns it gnvc the same result ns tlic formnldehydc method.(5) Substances resembling reductones in their renction to formnldehyde nre present in ccrtuin cnrnmelised or fermented foods. Thus, they have been found in dehydrated foods stored at temperatures in excess of 25'. They nlso occur in dehydrnted foods prepared n t temperntnrcs high enough to cnuse scorching of the ...

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