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![are of the correct type^ swni w^MT^tÖe seed—frtam which the recent etiquetares have ti^r^xu^. Their first structure (>wX kC'.f Le. ¿ts*f» ) consisted of a group of three parallel chains, each having a three-fold screw axis. The three chains were themselves related bv translations perpendicular to the fibre axis - or by a 3-fold screw axis; the two descriptions are equivalent. The chains were held together by hydrogen bonds between different chains. In their second paper Ramachandran and Kartha (195Ç ) modified this structure to conform to the correct xcrawx non-integer screw. This they did by giving an additional slow twist to their group of three ohains so that each chain, in addition to following a (roup-hlyO 7-Fold screw axis, also gradually coiled round the other two. In short, they proposed a coiled-coil structure. This basic idea we beleive to be correct, although the actual model they described %e] stereochemical^ impossible. Their model and the two models proposed here (Collagen I and II ) are all closely related. They differ only in the way the three chains are phased with respect to one another, and in particular in which hydrogen bonds are used to hold t e three chains together. These differences, however, are not trivial. Since our paper appeared Cowan, *cGavin and North (1956 ) have reported that they had been working on similar lines; Ramachandran (1955 ) has suggested that structure II is more likely to be i iqçi»; correct than Structure I ; and Bear^has described an alternative method of systematic model building which leads to Just the same the general](https://iiif.wellcomecollection.org/image/b18168504_PP_CRI_H_2_20_1_0002.jp2/full/800%2C/0/default.jpg)
