KINETIC METHODS 77 



1 1 Filler tube 



Buffer only 



■ 1 1 i 1 1 ill Mil 



• -•— : — 



Buffer plus 

 particles 



JL 



^ e. e. 



(a) 



(b) 



JL 



(c) 



Fig. 35. The setting up of a diffusion experiment. In (a) the lower tube has 

 been filled with a solution containing the particles whose movement is being 

 studied. The tube has flanged ground-glass ends. A similar tube is inverted 

 while empty onto the lower tube in a position such that the flange of one tube 

 covers the chamber portion of the other tube. The top tube is then filled with 

 the solution minus the particles. As shown in (b), the experiment is started by 

 sliding the top tube until the chambers are coincident. Particle diffusion can 

 then begin, and the particles can be found farther and farther up the tube as 

 time progresses. By placing a light-sensitive film behind the joined tubes, and 

 by shining light absorbed by the particles only from the front side, an absorption 

 image of the situation can be obtained at any time. 



the particle. Nevertheless, the electrically driven movement, the so- 

 called electrophoretic mobility, is characteristic for each particle in a 

 given solution, and can therefore be used to ascertain the presence or 

 absence of the particles. Further, one can find the number of electro- 

 phoretically different constituents of unknown solutions, and such infor- 

 mation frequently permits important deductions to be drawn. Still 

 further, electrophoretic separations may be used to prepare pure solu- 

 tions of these constituents. An important example concerns the study of 

 blood. When blood is subjected to an electric force, a number of con- 

 stituents are found in an entirely reproducible fashion. The constituents 

 are made visible by the boundary detection method described for diffu- 

 sion and sedimentation. The fastest moving substance has been isolated, 

 and turns out to be serum albumin. The next three fastest substances all 

 turn out to be globular proteins. In the order of speed, these have been 

 called alpha, beta, and gamma. The ignorance of particle size and shape 

 has not prevented investigators from finding that the entire antibody 

 content of blood is in the gamma globulin fraction. The electrophoretic 

 method is used to isolate this fraction for clinical use and for clinical and 

 laboratory research. 



