170 Organic Constituents of Saliva 



could be precipitated by dilute acetic acid, this criterion has been 

 used as a test for the presence of "mucin". Hammarsten (1888) 

 made a detailed study of methods of extraction of mucin from the 

 salivary glands and found that the most satisfactory method was to 

 extract with cold 0-1-0-2 per cent hydrochloric acid and then 

 dilute the extract with water when precipitation of the mucin 

 occurred. By this method 0-1-0-2 per cent of mucin is found in 

 submaxillary saliva and 0-5-1 per cent in extracts of submaxillary 

 glands; none is found in either parotid saliva or gland. McCrea 

 (1953) has found neutral extraction of dried submaxillary glands to 

 give less degradation of the polysaccharides. Komarov and Stav- 

 raky (1940) did not find that acetic acid or trichloracetic acid pro- 

 duced consistent or complete precipitation of the proteins in dog or 

 cat submaxillary saliva although it produced apparently complete 

 precipitation of the proteins of parotid saliva. They found that 

 reliable precipitation was obtained by the addition of two volumes 

 of acetone acidified with acetic acid. Araki (1951) confirmed this 

 finding and found that tungstic, metaphosphoric and sulphosalicylic 

 acids were also unreliable precipitating agents. He found that satura- 

 tion with ammonium sulphate was as satisfactory as acid alcohol or 

 acetone. These findings provide a glimpse into the complex species 

 differences between saliva proteins that make precipitation methods 

 of doubtful reliability. The safest way to prepare saliva protein 

 solutions from saliva is by ultrafiltration or equilibrium dialysis 

 followed by lyophilization. Anomalous precipitation reactions are 

 commonly found with a variety of mucoproteins and are presum- 

 ably due to interference with reactions satisfactory for ordinary 

 proteins by the hydrophilic properties of the carbohydrate residues 

 in the molecule. 



Viscosity in hyaluronate solutions and in synovial fluid has been 

 studied carefully by Ogston (Ogston and Stanier, 195 1 ; Blumberg 

 and Ogston, 1958). The hyaluronate particles in solution are very 

 dilute spheroids in which one gram of solid occupies a solute 

 volume of 200-500 ml. The viscosity of the solution is due to the 

 size of the particles and does not become excessive until overlap 

 between the polymer domains occurs, i.e. when the concentration 

 is greater than about 1 g/500 ml. In other words, as the molecular 

 domains overlap, the polysaccharide chains interpenetrate, form 

 larger aggregates and ultimately a rigid structure within which 

 virtually all the solvent is trapped. Ogston has come to the conclu- 



