IMPORTANCE OF ANTIBODIES IN DIAGNOSIS 389 



It will be observed from a study of the graph that at the time 

 ])oth animals were inoculated with virulent organisms the partially 

 immune rabbit's blood show^ed an agglutinin titer of 1:80 while 

 blood from the immune rabbit (No. 274) had a titer of 1 :160. The 

 agglutinin titer of neither animal was constant during the suc- 

 ceeding days, but varied as indicated by the graph. Blood cultures 

 were positive for the partially immune rabl)it on the ninth da>' 

 and for the immune animal on the twelfth day. In both aninuils 

 there was a drop in titer associated with blood stream invasion and 

 til is was followed by an increase in titer. 



It is interesting to note that the partially inununc animal died 

 on the eighteenth day wlien the titer had reached 1 :160, wliicli was 

 twice as much as at tlie beginning of the infection, while the titcc 

 for tlie immune animal stayed low (1:80) between the sixteenth 

 and the twenty-fourth day, when it began to increase. This lasted 

 several days, then dro])ped and finally Avent up to 1 :640 on the 

 fortieth day after the initial infection. 



Infection in Normal Animals.^ — The picture is quite different 

 in the normal animal. It shows that blood stream invasion occurs 

 much earlier and that no agglutinins can be demonstrated either 

 initially or during the infection. The failure to demonstrate 

 agglutinins is probably due to the fact that death usually occurs on 

 the fifth or sixth day which is too short a time for agglutinins 

 to appear. It is also interesting to note that the immune animal 

 did not show a high titer (1:160) when infection was produced, 

 but nevertheless, it survived blood stream invasion and completely 

 recovered. These results show lack of accurate correlation be- 

 tween antibody titer and immunity. 



The Effect of Specific Infection on the Titer of Ag'g-lutinin for 

 Other Organisms. — There are many specific infectious diseases 

 in which there occurs an increase in agglutinins for bacteria other 

 than the causal agent. This phenomenon is of importance in 

 typhus fever, tularemia, and also undulant fever. 



Felix- Weil Phenomenon. — Typhus fever is caused by certain 

 exceedingly minute organisms called Rickettsiae. They have been 

 successfully cultured by Nigg and Landsteiner (1932). Within 

 the ])lood stream of typhus patients there appear agglutinins for 

 a strain of B. proteus vulgaris called Proteus X19. The phenom- 



