M. A. LAUFFER 



First, the molecular weights were calculated using the Svedberg (23) 

 equatioft, M = RTS/[D{\ — Vp)\ where R is the gas constant, T 

 the absolute temperature, S the sedimentation constant, D the diffusion 

 constant, V the partial specific volume, p the density of the medium, 

 and M the molecular weight. From the molecular weights and the 

 partial specific volumes, the particle volumes were computed, and 

 from these the radii, ro, the particles would have if they were spheres 

 were calculated. From these radii the friction factors, /o, which the 

 particles would have if they were spheres were calculated by Stoke's 

 law, /o = 67r?7ro. The actual friction factors of the various protein 

 particles,/, were calculated from the diffusion constants by using the 

 Einstein-Sutherland (7) equation: / = RT/ND, where jV is Avogadro's 

 constant. The friction ratios, ///o, were then obtained. Perrin (18) 

 and others have shown from hydrodynamic considerations that, for 

 elongated ellipsoids of revolution: 



^.^ {b/aY^^ V\ - {a /by 



J J^ ~ / =^ 



1 + Vl - {alby 



In ; 



alb 



and for flattened ellipsoids of revolution: 



^{hlaY - 1 



///o = 



(V«)'^'arctanA/(Vfl)2 - 1 



Thus, with///o determined from experimental data, h/a values were 

 calculated on the assumption that the particles were (1) elongated 

 ellipsoids of revolution and (2) flattened ellipsoids of revolution. The 

 data considered by Mehl el al. are presented in Table III. 



An obvious ambiguity exists in the interpretation of these data, 

 for it is possible to assume either a rodlike or a platelike ellipsoid as 

 the model for a protein molecule, unless independent evidence con- 

 cerning the shape is available. In general, however, it can be seen 

 that the viscosity data interpreted by the Simha equation are in better 

 agreement with the diffusion and sedimentation data as interpreted by 

 the Perrin equation when rodlike ellipsoids of revolution are assumed 

 to represent the shapes. 



A far more serious source of ambiguity is derived from the fact 

 that Mehl and co-workers had to assume that the particles were un- 



