THE FIXATION OF ALEXINS. 349 



Tube 1. First NaCl washing solution 0.2 c.c. 



Serum rabbit > ox, 55 degrees* 0.6 c.c. 



Tube 2. Second NaCl washing solution 0.2 c.c. 



Serum rabbit > ox, 55 degrees 0.6 c.c. 



Tube 3. Fresh NaCl solution 0.2 c.c. 



Serum rabbit > ox, 55 degrees 0.6 c.c. 



Tube 4. First NaCl washing solution 0.2 c.c. 



Serum normal rabbit, 55 degrees 0.6' c.c. 

 Tubes are left at room temperature 2 hours. 

 In tube 1. Abundant precipitate. 

 In tube 2. Trace of precipitate. 

 In tubes 3 and 4. No precipitate. 



Tube 1 is then centrifugalized and the supernatant fluid forms 

 tube la, while the precipitate is brought to the original volume 

 (0.8 of a cubic centimeter) with salt solution and forms Tube 1. To 

 each of the tubes 1, la, 2, 3 and 4 is then added fresh rabbit serum 

 (24 hours), 0.075 of a cubic centimeter, and contact allowed for 2 

 hours at room temperature. To each tube is then added 0.025 of a 

 cubic centimeter of sensitized rabbit corpuscles (S. rabbit > ox, 

 55 degrees), and the resultant hemolysis is as follows: 



Tube 1 (precipitate). No hemolysis. 

 Tubes la, 2, 3 and 4. Hemolysis complete. 



This experiment shows clearly that it is the specific precipitate 

 that fixes the alexin. In tube 2 the hemolysis, although finally 

 complete, is distinctly delayed owing to partial absorption of the 

 alexin by the very slight precipitate. 



The marked difference in dosage between the precipitinogen and 

 the precipitin is indicated by the dilutions of ox serum represented 

 by the washing solutions of the last experiment. In fact, very 

 small traces of the precipitinogen suffice to give a maximum pre- 

 cipitate, provided sufficient immune serum (precipitin) is used. 

 A more accurate idea of the relation of dosage and dilution between 

 the two precipitate-forming sera than is given incidentally in the 

 following experiments need not concern us here, since we are to deal 

 rather with the properties of precipitates than with their formation. 



The question may properly arise as to whether the sensitizing 

 activity of the immune body for the corpuscles has been diminished 

 by the formation of a specific precipitate, and is directly answered 

 by the following experiment: 



* Which abbreviation is used to indicate the serum of a rabbit immunized 

 against ox blood. Such serum, as indicated, has been heated to 55 C for 

 one-half hour to deprive it of alexin. 



