A Method for the Concentration of Influenza Virus.

A LLANTOIC fluid from eggs infected with influenza A virus is slightly milky and opalescent in appearance. When it is frozen and allowed to melt slowly and without agitation, a fluffy white precipitate appears at the bottom of the tube, leaving a water-clear supernatant fluid above. This precipitate only appears if the fluid is allowed to melt undisturbed and at a temperature a little above its freezing point. If it be warmed to 37 °C. and agitated, the precipitate usually disappears and the fluid resembles that which has been freshly drawn. Examination of the clear supernatant fluid obtained after freezing and slow thawing showed that there was considerably less virus in it than in the original allantoic fluid, and, as will be shown below, there is evidence that the bulk of the virus is carried down on the precipitate. As this phenomenon appeared to be a possible method for the concentration and purification of the virus, it was studied in detail.