232 IMMUNOLOGY 



with the naked eye and with a reading glass. Tliere appeared at 

 once in tubes 7 to 2 a cloudy opalescence; after five minutes the 

 opalescence was obviously more marked in the center tubes of the 

 rack and tubes 6 and 5 were leading. After twenty-five minutes 

 tubes 6, 5, and 4 were ahead of the others. 



Tube Five Contains Optbial Proportions. — In tube 5 discrete 

 particles formed earlier than in any other tube; within thirty 

 minutes the particles of tube 5 were larger than those of tube 6 or 

 tube 4. Particles were present in all the tubes after forty-five 

 minutes. The largest particles were in tube 5, next largest in tube 

 4, then in tubes 6 and 3. Tube 5, the first tube to show distinct 

 particles, contained 0.00125 c.c. of horse serum. The proportion of 

 antigen to antibody in this tube was 1 to 20, i.e., as 0.00125 is to 

 0.025. In general, they found that strong or quickly acting anti- 

 sera could be used in a dilution of 1 in 40. 



Unit Suggested by Dean and Webb. — In regard to applying 

 this test to a quantitative estimation of antibody, Dean and Webb 

 (Dean, 1931) reason that it is possible to express the antibody 

 content in units if the ratio figure depends on the antibody con- 

 tent of the serum. To do this they assume that a unit of anti- 

 body is contained in the volume of antiserum which forms distinct 

 particles most rapidly with 0.00001 c.c. of normal horse serum. 

 To illu.strate the significance of the results, they state that if the 

 optimal antigen-antiserum ratio is found to be 1 :200 it indicates 

 that 0.00001 c.c. of horse serum would react with 0.002 c.c. of anti- 

 serum (200 times its volume). Therefore 0.002 c.c. of antiserum 

 contains one unit of antibody and one cubic centimeter Avould 

 contain 500 units of the latter. (Dean, 1931, p. 430.) From this 

 it is obvious that a low antigen-antiserum ratio figure indicates 

 that the antiserum is rich in antil^ody while a high figure indicates 

 the reverse. 



Precipitins Used to Estimate Haptens and Proteins. — ^Heidel- 

 berger (1933) has reviewed tlie recent literature on precipitins 

 and calls attention to the use of methods, based upon Dean and 

 Webb's optimal proportions procedure, in the estimation of pro- 

 teins and also specific polysaccharides. 



Reason for Coexistence of Antigen and Antibody in Blood. — 

 Dean (1931) suggests that perhaps the reason that antigen and 



