328 PHYSICAL PROPERTIES 



the gelatin is partially destroyed by heating. Garrett has also 

 found that in a solution of gelatin which had been boiled the 

 logarithmic decrement of an oscillating disc does not increase with 

 time. 



According to Lichtwitz and Renner (61) the viscosity of serum 

 albumin solutions falls with rising temperature from 15 to 60° C. 

 in the same proportion as the viscosity of water. Chick and 

 Lubrzynski (20) have also shown that the influence of tempera- 

 ture upon the viscosity of egg-albumin solutions containing up to 

 20 per cent of protein is slight and a linear function of temperature 

 being similar to the influence of temperature upon the viscosity 

 of a solution of a crystalloid. In solutions containing a higher 

 percentage of protein, however, the relationship between viscosity 

 and temperature is curvilinear, the decrease being most rapid at 

 low temperatures. From these results it would appear reasonable 

 to infer that a change of temperature at temperatures lying below 

 those necessary to induce coagulation affects the viscosity of a 

 protein solution chiefly through altering the viscosity of the solvent, 

 a deduction which is in harmony with the view expressed above 

 that proteins in solution are not in any large proportion present 

 therein in the form of independently mobile particles. 



It has been shown by Christiansen (22) that acid protein solu- 

 tions attain a maximum of viscosity when a slight excess of free 

 acid is present, presumably coinciding approximately with the 

 attainment of maximum combining capacity for the acid. The 

 acidity which produces maximum viscosity is also the optimum 

 acidity for the digestive action of pepsin. The viscosity of the 

 solution decreases during digestion, a fact which had previously 

 been demonstrated by Spriggs (116). 



2. The Cohesiveness of Protein Solutions. — Closely allied 

 to the property of viscosity is the property which may be somewhat 

 vaguely designated "cohesiveness." The influence of a variety of 

 aqueous solutions of acids, bases and salts upon the cohesiveness of 

 gluten has been investigated by Wood and Hardy (132). These 

 observers prepared gluten by washing flour in a stream of water 

 to remove the starch. The protein residue is a coherent stringy 

 mass, insoluble in water and consisting essentially of a mixture of 

 gliadin and glutenin (Cf. Chap. II). The action of solutions upon 

 the cohesiveness of the gluten was estimated quantitatively by 

 suspending a small mass of gluten on a bent glass rod in a beaker 



