330 Scientific Proceedings (130) 



mixing with antigen. This renders the final antigen-salt solution 

 mixture somewhat less stable than mixtures prepared with salt 

 solution kept at room temperature. 2. Instead of mixing 3 parts 

 of salt solution with 1 part of antigen, 2.5 parts of salt solution 

 are mixed with 1 part of antigen. This increases the instability 

 of the final mixture with reference to precipitation. We have 

 not had occasion to use less than 2.5 parts of salt solution with 

 1 part of antigen in our work. 



The important thing to keep in mind is that the antigen-salt 

 solution mixture used in the tests must show no signs of tur- 

 bidity. An antigen mixture showing even slight turbidity will 

 be likely to give false weak reactions. 



Procedure II (Modified) 

 Principle : The mechanism of this procedure is believed to be 

 somewhat different from that of procedure I. Antigen and salt 

 solution are mixed in such proportions that the major part of 

 the lipoids is precipitated in a very fine state. The precipitate is 

 obtained free from other elements by centrifugation. On resus- 

 pending this precipitate in salt solution, there results a milky but 

 opalescent mixture. This mixture shows no trace of visible pre- 

 cipitate but undoubtedly consists of a suspension of lipoid par- 

 ticles in a very fine form, and when mixed with serum is appar- 

 ently capable of combining readily with the specific elements of 

 the latter. (The application of this principle to other antigens 

 will be discussed in forthcoming studies). 



Dilution of Antigen for Tests : 



1. A given amount of antigen (depending on number of 

 tests) is measured into a small tube and an equal amount of salt 

 solution is added to it either from a pipette or from another 

 tube. 



2. This is mixed and centrifuged for about five minutes — 

 until the supernatant fluid is practically clear and a white pre- 

 cipitate is settled on the bottom of the tube. 



3. The supernatant fluid is poured off and discarded and the 

 amount replaced with salt solution. (Ex. : 0.5 c.c. antigen is mixed 

 with 0.5 c.c. saline and centrifuged. Supernatant fluid is poured 

 off and 1 c.c. saline added). 



4. On mixing, the precipitate is redissolved in the salt solution, 



