2d6 IMMUNOLOGY 



that a similar mechanism operates in tlie precipitin reaction. Here 

 the antigen is a protein in colloidal solution which, because of the 

 smallness of colloidal particles, permits of great surface exposure 

 per unit of mass. The significance of this can best be appreciated 

 by the following example : If a cube of solid material one 

 centimeter on each side, i.e., 1 c.c. in volume and hence having a 

 surface area of 6 sq. cm., is divided into 1,000,000,000,000,000 

 smaller cubes each being 0.0001 mm. on the side, the total surface 

 would be increased from 6 square centimeters to 6,000 square 

 centimeters. If, however, the original cube is divided into still 

 smaller cubes, each having a side length corresponding to the 

 minimum dimensions of colloidal particles, tlie total surface ex- 

 posed would be increased from the original 6 sfjuare centimeters to 

 14.83 acres. Zinsser (1930) estimates that if a bacterial cell were 

 divided into particles the size of the antigenic particles in colloid 

 solution, the total surface exposed would be increased 10,000 times. 



It Avill thus be seen that in the precipitin reaction the antibody 

 globulin is being filmed upon colloidal particles or aggregates 

 of antigen and because of the colloidal state of the antigen, the 

 surface to be filmed is relatively much greater than in the case 

 of the filming of bacteria for agglutination. For this reason the 

 antigen can be highly diluted, l)ut the antibody globulin can be 

 diluted only moderately if it is to film the antigenic particles 

 adequately. 



The method suggested by Cannon et al. reduces the surface of 

 antigen by filming it onto collodion particles and tlnis permits of 

 a real titration of the antibody. It is a more rational method than 

 the ring technique. 



References 



Baier, .J. G.: Quantitative Studies on Precipitins. Reprint from Physiol. 



Zool. 6: 91, 1933. 

 Bancroft: Colloid Symposium Monograph, New York, Chemical Catalogue 



Co. 4: 29, 1926. 

 Barenberg, L. H., Lewis, J. M., and Messer, W. H.: Measles Prophylaxis: 



Comparative Results with Use of Adult Blood, Convalescent Serum, 



and Immune Goat Serum, J. A. M. A. 95: 4, 1930. 

 Bayne-Jones, S. : The Titration of Toxins and Antitoxins by the Floccula- 



tion Method. Newer Knowledge of Bacteriology and Immunology, 



Chicago, 1928, University of Chicago Press, p. 759. 

 Bordet, J.: Studies in Immunity, Bordet and Gay, New York, 1909, John 



Wiley & Sons, Inc. 

 Bordet: Cited in Kraus and Levaditi, Hand, der Tek. u. M«th., Jena, 



1907, Gustav Fischer. 



