MUCOPOLYSACCHARIDES OF CONNECTIVE TISSUE 329 



and protein is not yet established, it appears unlikely that a covalent bond 

 exists [6]. Hyaluronic acid occurs in a large number of mammalian tissues. 

 The presence of hyaluronic acid in the capsule of Group A streptococci 

 is unique. Polysaccharides of similar structure are found in capsules of 

 other microorganisms, but in no other authenticated case is the capsular 

 substance identical with a mammalian polysaccharide. The biological 

 function of hyaluronic acid is not clearly delineated; it is neither anti- 

 thrombic nor anticoagulant. Hyaluronic acid appears together with other 

 mucopolysaccharides in a number of connective tissues, but seems to be 

 characteristic of tissues with high water content. It is the principal poly- 

 saccharide of vitreous humour, synovial fluid, Wharton's jelly of umbilical 

 cord, cock's comb, and sex skin of certain primates. As will be demon- 

 strated below, thyroid deficiency with its concomitant oedema is charac- 

 terized by an increase in hyaluronic acid. While this association is highly 

 suggestive, its significance is not entirely clear. The specific association of 

 tissue hydration with hyaluronic acid rather than with the sulphated 

 polysaccharides is not readily explained on the basis of osmotic considera- 

 tions. Reinits [7], in a study of the rate of accumulation of hyaluronic acid 

 and water in the sex skin of certain primates found that hydration precedes 

 the peak of hyaluronic acid accumulation. He suggests that hyaluronic 

 acid serves to induce an accumulation of protein in the extracellular space 

 by hindering the access of protein to the lymph capillaries, with the con- 

 sequent increase in osmotic pressure due to the proteins. Reinits 's experi- 

 ments may be open to criticism on the basis of the inadequacy of the 

 methods for estimation of hyaluronic acid. Fessler [8] has emphasized the 

 role of hyaluronic acid in forming a system of relative non-compres- 

 sibility as a result of the interaction of a viscous solution with intermingled 

 collagen fibres. However, this study establishes no specificity for hyaluronic 

 acid in contradistinction to other acid mucopolysaccharides. That hyaluronic 

 acid does afford a mechanical barrier is attested by the action of hyaluroni- 

 dase in promoting the spread of particulates. 



The association of hyaluronic acid with tissue hydration may be 

 attributed to the fact that hyaluronic acid is bound less avidly with protein 

 than are the sulphated polysaccharides. Insufficient data are available for 

 localizing individual polysaccharides in tissues which contain mixtures. It 

 is possible that the sulphated polysaccharides are more closely associated 

 with structural elements while hyaluronic acid is present in higher con- 

 centration in the amorphous gel between these elements. Mathews [9] 

 has demonstrated a strong afiinity of the chondroitin sulphuric acid 

 protein complex for collagen. 



Chondroitin sulphuric acids-A and -C are present in largest con- 

 centration in cartilage and appear to be responsible to a considerable 

 degree for the unique physical characteristics of this tissue. The possible 



