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Scientific Proceedings (78). 



was especially brought out in the beginning of the present war, 

 when it became necessary to differentiate between the soldiers 

 who gave positive Widal reactions due to previous prophylactic 

 vaccinations, and those actually infected, or those who may be 

 carriers. It was suggested by German authors that the comple- 

 ment deviation test may solve this problem in so much as, in their 

 experience, artificial immunization by means of a vaccine, although 

 followed by the development of agglutinins, did not seem to 

 influence the production of the complement-fixing antibody in any 

 marked degree. This suggestion was followed up in many labora- 

 tories abroad as well as in this country. In our own laboratory, 

 for instance, this question was studied during the last two years 

 by Doctors G. C. Simpson and J. R. Johnston, but the conclusions 

 drawn were not very encouraging. The necessity of differentiating 

 between actual disease and the state of immunity is not limited to 

 the case of typhoid. Since it has become the practice in large 

 institutions to apply the Shick test, it has also become necessary 

 to differentiate between individuals containing antitoxin in their 

 blood as a result of natural immunity and those who may be 

 harboring a mild infection or those who may be carriers. In 

 case of diagnosis of gonnorhea many workers have noticed that 

 often very old cases without any symptoms of the o'd infection 

 for many years, still frequently give a positive complement devia- 

 tion test. The same is true for tuberculosis, syphilis and, in fact, 

 for any infectious disease, for antibodies are known to persist in 

 the blood for a certain length of time after the actual recovery 

 from the infection. It is evident that if it were possible in addition 

 to detection of antibody in the blood to detect also the antigen, 

 where it is present, it would permit one to differentiate the condi- 

 tion of disease in its incubation period or in its mild course, from 

 the condition of immunity, following the disease or artificial 

 immunization. 



Recently, in the midst of other work, which will follow later, 

 we have made an observation which seems to indicate this possi- 

 bility. We noticed that in certain stages of different infectious 

 diseases the antigen and antibody coexist in the blood and may 

 cause the fixation of complement. The fluctuations in the com- 

 plement content of the blood we.e noticed long since, but the 



