JACQUES LOEB 79 



electric gelatin solution stand for 3 hours at 20°C. before adding the 

 acid, we get a parallel curve but higher than the first one (middle 

 curve, Fig. 3), for the reason that during the 3 hours an additional 

 number of solid jelly particles capable of swelling has been formed. 

 If we let the solution of isoelectric gelatin stand for 17 hours at 20°C., 

 the curve (upper curve, Fig. 3), is still higher though practically 

 parallel with the first curve except at the summit. It is probable 

 that on standing the size of individual particles also increases and 

 the greater the size the greater the viscosity, since the viscosity is 

 chiefly but not exclusively a function of the relative volume of the 

 particles. 



These and similar experiments agree with the occlusion theory 

 but not with the hydration theory; since there is no reason why the 

 degree of hydration of gelatin should increase the longer isoelectric 

 gelatin is kept at 20°C. 



3. The fact that the viscosity of certain protein solutions is compar- 

 atively high, especially in the case of gelatin, has led to the suggestion 

 that proteins might possess a different type of viscosity not present in 

 solutions of crystalloids and that this second type of viscosity might 

 be connected with a certain structure in the protein solution. 



" Bearing in mind the possibility that protein solutions may contain 

 a preformed molecular structure analogous to that of the jellies or 

 coagula which they can form, we are strongly impelled towards the 

 belief that the type of viscosity which solutions of proteins exhibit 

 may in some manner owe its existence to this structure, and not to 

 the type of internal friction which hinders molecular and ionic motion. 

 Thus a netlike structure, such as a tennis net, will offer no hindrance 

 to the passage through it of a quickly moving body which is smaller 

 than its meshes, other than that which is due to the fact that the 

 material which composes the net occupies a small fraction of the 

 area which the body must traverse, but to any force which involves 

 deformation of the structure, for instance, a force which seeks to 

 drag it through a small tube, it will offer a very considerable 

 resistance."^ 



^Robertson, T. B., The physical chemistry of proteins, New York, London, 

 Bombay, Calcutta, and Madras, 1918, 324-325. 



