The swelling of structured proteins - The influence of the reticular tissue on the swelling of collagen in water and hydrochloric acid

Previous observations on the swelling of fibrous tissues and fibres (Kaye and Jordan-Lloyd, 1924, a ; Marriott, 1932; Jordan-Lloyd, Marriott, and Pleass, 1933; Jordan-Lloyd and Marriott, 1933, 1934) have shown that the swelling of biological material is largely influenced by its structure. Even a fibre that is histologically structureless, as, for example, a fibre of silk-fibroin (silk-gut), can be shown to consist of a number of fine fibrils held together by lateral cohesive forces. Both with silk fibres and keratin fibres (horsehair), the evidence suggests that the structure of the fibre is maintained by what may be described as an equivalent of a system of internal girders, these girders being the lateral cohesive forces between the molecules. Keratin fibres (hairs) are of cellular origin, though a fibrous rather than a cellular structure exists in the hair shaft. Collagen fibres are also of cellular origin, though in their fully developed form they are by no means such rigid structures as silk fibres or hairs, and swell much more freely. It has been shown already that the swelling of collagen fibres, while woven together to form the tissue of the skin, depends both on the structure of the fibres and on the pattern of the weave, skin pieces where the weave is loose swelling more freely under the same conditions than skin pieces where the weave is more compact (Kaye and Jordan-Lloyd, 1924). Moreover, it has also been shown that if the fibres were invested with a film of coagulated protein, swelling was less than under fresh conditions. Swelling is, therefore, also a function of the external stresses exerted on the fibre, a generalization confirmed by Marriott (1932) in a study of the behaviour of single collagen fibre bundles teased out of the skin tissue. Collagen fibres cannot be obtained free from all other tissues. They are invested and held together throughout the skin by another fibrous protein, the reticular tissue (Kaye, 1929; Kuntzel and Prakke, 1933). This tissue forms the equivalent of a system of external girders round the actual collagen fibres and influences their behaviour. Collagen fibres from skin which were used in the earlier work are not a suitable material for the study of the influence of the reticular tissue on the swelling of collagen owing to the difficulty of teasing out a good supply of undamaged, suitable single fibres in a reasonably short space of time from fresh skin. For this reason the tendons from rats’ tails were selected for study. Previous work on the swelling of tendons has been recorded by Kuntzel (1926) and of their structure by Kuntzel and Prakke (1933).