JACQUES LOEB 



77 



temporarily the density of the suspension.) After the viscosity of 

 a suspension was measured, the suspension was transformed into a 

 solution by heating the suspension to 45° for 10 minutes; after that 

 the solution was rapidly cooled to 20° and the viscosity of the gelatin 

 solution was now measured with the same viscometer. The lower 

 curve in Fig. 2 shows that the viscosity was now considerably 

 diminished. The abscissae are the pH of the gelatin solutions. 



pH 1.6 1.8 2.0 2.2 2.4 Z6 2.8 3.0 3.2 3.4 3.6 3.6 40 42 



Fig. 2. Difference in the viscosity of a suspension of 0.5 gm. of powdered 

 gelatin in 100 cc. and of the solution of the suspension in the same liquid; both 

 viscosities were measured at 20°C. 



Another test of the occlusion theory of viscosity is as follows. 

 When we heat a 1 per cent solution of isoelectric gelatin rapidly to 

 45° and cool it rapidly to a lower temperature, e.g., 20°C., the solution 

 will ultimately set to a continuous gel but will steadily increase its 

 viscosity before this stage is reached. It is natural to assume that 

 the formation of a continuous jelly is preceded by the formation of 

 smaller masses of jelly, which at first are submicroscopic and later 



