Viruses 407 



stages of suspected influenza, it is possible to measure differences 

 in antibody titers of the sera by an agglutination-inhibition test. 

 That is, by taking a known concentration of influenza virus which 

 will clump chicken red blood cells to a known titer, and by adding 

 serum from the patient, specific antibodies for influenza will inhibit 

 the agglutination of chicken cells when the mixture of virus and 

 blood serum is tested against the blood cells. A marked increase 

 in inhibition of the convalescent patient's serum over the reaction 

 of the acute serum is indicative that the patient had influenza and 

 has built up specific immune substances against the virus. 



