Precipitation of Diphtheria Antitoxin. 149 



Injections and development of aniisera. — Nine rabbits were immunized against 

 diphtheria antitoxic globulin and eight against normal serum globulin as follows: 



Antitoxic globulin, preparation No. 163. 

 Injections begun March 7, 1909. Three rabbits injected at intervals of three days. 

 No. 1 — 4 injections of 2.5 c.c. produced an immune serum of 1/20,000 strength. 

 No. 2 — 6 injections of 2.5 c.c. produced an immune serum of 1/20,000+ strength. 

 No. 3 — 9 injections of 2.5 c.c. produced an immune serum of 1/30,000+ strength. 



Injections begun May I, 1909; 2 rabbits subcutaneously. 



5 injections, each of 2.5 c.c. every 2 days. 

 Injections begun December 2, 1909; 2 rabbits. 



6 injections, each 2.5 c.c. 



Normal serum globulin. 

 Injections begun March 24, 1909; 3 rabbits injected every 3 days. 



No. 1 — 5 injections of 2.5 c.c. 



No. 2 — 5 injections of 2.5 c.c. 



No. 3 — 9 injections of 2.5 c.c. 

 Injections begun May I, 1909; 1 rabbit subcutaneously. 



5 injections of 2.5 c.c. every 2 days. 

 Injections begun December 2, 1909; 2 rabbits. 



5 injections each of 2.5 c.c. 

 The rabbits were bled ten days after the final injection. It was not considered 

 necessary to test the strength of the immune sera after the first tests, since it was 

 all needed for the experimental work. 



Two explanations are applicable to these reactions. 



1. Diphtheria antitoxin is a globulin which is not changed by 

 heat to a form insoluble in saturated solution of sodium chloride 

 and is consequently precipitated by a globulin antibody of the 

 same nature. We have not yet tried the effect of the addition 

 of an antibody for pure eu-globulin on diphtheria antitoxin. 



2. Diphtheria antitoxin is carried down mechanically in the 

 precipitation of the globulin by the antibody as a mordant carries 

 a dye out of solution and holds it. 



If the first explanation is true then the combination of the 

 diphtheria antitoxin with the antibody is a comparatively loose 

 one, because normal saline solution and glycerine partially separate 

 them, and the precipitate will neutralize diphtheria toxin. 



If the second explanation is true, the precipitation of the globu- 

 lins by means of a precipitin acts as a very complete and powerful 

 mordant, using the term "mordant" in the broad sense of a cleaning 

 agent. 



