Sensitivity of human-cell cultures to soft x-rays.

serious restrictions on the extensibility of the spiral. I t may be calculated from columns 3, 4 and 5 of Table I that the cystine content of Fraction I corresponds to approx, only I cystine residue/3o non-cystine residues, whereas the average for wool is i :i6. This favours the possibility that the cystine is intra-linked in Fraction I and corresponds to the AB cystine fraction of PHILLIPS. The wool fraction known as fl-keratose, which morphologically consists of the cortical-cell membranes, has not been considered in this survey. This material remains insoluble in dilute ammonia after wool has been oxidized with peracetic acid. Analytically it is very similar to a-keratose 7 and it is probably insolublized by a small degree of cross-linking, although this has not been proved. Its omission does not affect any of the views presented. C. EARLAND Department o[ Textile Industries, A. WISEMAN* Institute o/Technology, Brad/ord (Great Britain)