PRECIPITINS 231 



Dean and Webb (1926) have developed a method for the quan- 

 titative determination of either antigen or antibody depending 

 upon the optimal ratio of one to the other within the mixture. 

 This is called the Optivwl Proportion Method. 



Coarse Test of Dean and Webb. — In this test they first de- 

 termine the titer i-oughly by preparing four dilutions of anti- 

 serum, i.e., 1 :5, 1 :10, 1 :20, and 1 :40 and ten sets of dilutions of 

 antigen ranging from 1:10 to 1:10,000. Dean and Webb (1926) 

 state that the volume of horse serum dilution in each set is 1 c.c, 

 and the quantity of horse serum is halved progressively in each 

 tube of the series. To each tube of set A they add 1 c.c. of un- 

 diluted antiserum, to each tu])e of set B, 1 c.c. of 1 to 5 dilution of 

 antiserum. They include as controls one set of antigen and also 

 tubes containing only antiserum and saline, the two latter to serve 

 as antiserum controls. 



Optbial Proportions Fine Test. — The object of the experiment 

 is to determine which tube in each set containing varying mix- 

 tures of antigen with antibody shows the most rapid formation of 

 a precipitate In this way they determine the mixture in which 

 the speed of the reaction is greatest. For the experiment cited 

 they found that the optimal ratio of antigen to antiserum was 

 between 1 :16 and 1 :32. With this information they proceeded to a 

 finer titration. TliLs is described by Dean and Webb (1926) very 

 much as follows : They prepared an initial 1 :100 dilution of horse 

 serum (antigen) using a 100 c.c. volumetric flask. Ten tubes were 

 placed in a rack and numbered for convenience 10 to 1 from left 

 to right. A dilution suitable for tlie test was prepared from the 

 initial 1 in 100 dilution: in tliis case 1 in 400 was used. Of this 

 1 in 400 dilution, quantities varying from 1 c.c. to 0.1 c.c. were 

 jiipetted into each of the ten tubes. The difference betwceji eacli 

 tube was therefore 0.00025 c.c. of horse scrum. The volume in each 

 tube was made up to 1 c.c. l)y adding an appropriate volume of 

 saline solution. One cubic centimeter of a 1 in 40 dilution of anti- 

 serum was added to every tube. Thus the volume of antiserum in 

 each tube was 0.025 c.c. Controls were also included. The rack 

 containing the tubes in a single line was incubated at room tem- 

 perature and observed constantly. The progress of precipitation 

 was watched against a dark background properly illuminated by a 

 shielded electric light. The formation of precipitate was observed 



