490 



Scientific Proceedings (132) 



With most antigens, three parts of salt solution represent the 

 minimum amount which will bring about an opalescent mixture. 

 In some cases, however, 2.5 and even 2 parts of salt solution 

 may still produce an opalescent mixture and may therefore be 

 used with safety. An antigen-salt solution mixture must show 

 no signs of turbidity when used in the tests. 



Those tubes showing precipitation are now centrifuged for 

 about 10 minutes, supernatant fluid poured off and replaced with 

 an amount of salt solution (1 c.c.) equivalent to twice the amount 

 of antigen originally used. After thorough shaking, it will be 

 observed that whereas the tube which originally contained 0.5 

 c.c. antigen and 0.25 salt solution shows a precipitate, the next 

 tube which contained equal quantities of antigen and salt solu- 

 tion, although milky, may be opalescent and entirely free from 

 any suggestion of a precipitate. If this tube shows some tur- 

 bidity instead of opalescence then the next tube which contained 

 0.5 c.c. antigen and 0.7 c.c. salt solution will be found to be 

 opalescent. Under such conditions one is also likely to find that 

 an antigen-salt solution proportion of 1 :1 .25 (instead of 

 1 :1.S) will also produce opalescent mixtures and could there- 

 fore be used in the tests. 



The salt solution-antigen proportion in which the smallest 

 amount of salt solution produces a precipitate capable of form- 

 ing an opalescent mixture on resus pension in salt solution is 

 the antigen-salt solution titre in procedure II. 



Table I illustrates a typical titration of antigen. 



TABLE I. AXTIGEX TITRATION. 



Tube 



1 



2 



3 



4 



5 



6 



Antigen c.c. 



0.5 



0.5 



0.5 



0.5 



0.5 



0.5 



Salt Solu- 















tion c.c. .. 



0.25 



0.5 



0.75 



1.0 



1.25 



1.5 



The antigen and salt solution 



are mixed in each case by pouring the 



latter into the antigen tube and immediately pouring the mixture 



back and 



forth several 



times. 













Results 



Precipi- 



Precipi- 



Precipi- 





Opal- 



Opal- 



tate 



tate 



tate 



Cloudy 



escence 



escence 



Tubes 1 



2 and 3 



are now centrifuged 



for about 



10 minutes, super- 



natant fluid poured off, 



replaced with 1 c.c. salt solution (twice the amount 



of antigen originally employed) and mixed 



thoroughly. 







Results 



Precipi- 



Opal- 



Opal- 





1 





tate 



escence 



escence 





1 





