Viscosity and composition of solutions derived from rabbit vitreous humour.

THERE are three kinds of macromolecular substance in the vitreous humour: fibrous material, a viscous mucopolysaccharide, and soluble protein. The first, the residual protein, has many properties in common with collagen (Pirie, Schmidt, and Waters, 1948). The second, hyaluronic acid, has been characterized by Meyer and Palmer (1934) and shown to be a polymer of glucuronic acid and N-acetyl glucosamine. The last, the soluble protein, has some characteristics in common with serum proteins (Varga and Balazs, 1954; Brunish, Rowen, and Irvine, 1955), but the identity of the two has yet to be proved. These materials are present in very small amounts. Ox vitreous, for example, contains only about 012 per cent. colloids. Since the colloids are so dilute, it appeared probable that the stability of the gel was due not to water-binding by the isolated molecules but to their interaction to produce a network. We have obtained evidence to support this from a study of ox vitreous humour (Woodin and Boruchoff, 1955). Thus when ox vitreous is solubilized by high-speed stirring, the resultant liquid exhibits anomalous viscosity. Anomalous viscosity is the dependence of the viscosity on the forces applied to the liquid and it is a sign of the tendency of the liquid to form a gel. We found that the anomalous viscosity of ox vitreous is due to interaction between the hyaluronic acid and the residual protein, soluble protein playing little part in the process. The interaction is not due to specific chemical bonds but may be explained in terms ofthe size and charge of the particles. It will be shown in this paper that rabbit vitreous humour has a much smaller concentration of hyaluronic acid and a somewhat larger concentration of residual protein than ox vitreous humour. Therefore some preliminary experiments in vitro on the factors determining the stability of rabbit vitreous humour were carried out. The stability in vivo was also of interest. Von Sallman (1948) showed that injections of hyaluronidase into vitreous humour caused an inflammatory response and facilitated the movement of injected red blood cells. Pirie