A number of experiments were performed on the adsorption of influenza hemagglutinins on chicken red blood cells, from which the following conclusions were drawn:—

1. When chicken red blood cells and preparations of influenza viruses were mixed together, the influenza hemagglutinins present were rapidly adsorbed onto the cells. After varying lengths of time, dependent on the conditions of the experiment, the adsorbed hemagglutinins began to elute from the cells. With the Lee strain at 23°C. and the PR8 strain at 37°C. almost all of the adsorbed agglutinin was released in 4 to 6 hours.

2. When the number of red cells used for adsorption was increased, the speed and degree of adsorption of the hemagglutinins increased. The time of maximum adsorption of hemagglutinins was the same, regardiess of red cell concentration, and with the larger amounts of red cells the speed and degree of elution was decreased.

3. When adsorption of PR8 virus agglutinins was carried out at 4°C. the adsorption was rapid and nearly complete. When the reaction was carried out at higher temperatures (27° and 37°C.), the adsorption was equally rapid but was progressively less complete with rise in temperature. At 4°C. the maximum adsorption was not reached for 5 hours; at 27°C. it was reached in 25 minutes; and at 37°C. the greatest degree of adsorption was attained between 3 and 5 minutes. The amount of elution observed at 4°C. at 18 hours was negligible, but the degree of elution increased with temperature so that at 37°C. almost all of the adsorbed agglutinin was released in 6 hours' time.

4. Red cells which had adsorbed and then fully eluted the agglutinin were not capable of adsorbing a detectable amount of fresh agglutinin. In addition, such cells would no longer agglutinate even though exposed to fresh virus suspensions.

5. The hemagglutinin of influenza B virus was capable of being adsorbed on and eluted from several successive lots of chicken red cells without appreciable loss of agglutinating activity.

6. The hemagglutinins of the PR8 and Lee strains were rapidly inactivated at 60°C. The presence of active virus was not necessary for the occurrence of the adsorption-elution reaction on chicken red cells.

7. The activity of the portion of the red cells responsible for the adsorption of the hemagglutinins persisted, though in reduced amount, even after heating for 5 minutes at 100°C. Hemagglutinins were adsorbed and eluted from red cell stroma.

8. The infective agent in influenza virus suspensions was adsorbed by chicken red cells simultaneously with the adsorption of hemagglutinins. 95 per cent of the infective agent was removed from suspension by the red cells after contact for 15 minutes. From then on the infective agent was gradually released from the red cells. After 4 hours the 50 per cent mortality titer of the supernatant fluid was as high as at the beginning of the experiment.

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