Helenine is moderately stable in solution at refrigerator temperature and can be kept for long periods of time without evident loss of activity if stored frozen at the temperature of solid CO2. It is filterable through a Seitz pad but not dialyzable. Crude SPS preparations of helenine do not lose activity when dried from the frozen state. Some conditions are described, however, which influence the preservation or inactivation of acetone-precipitated helenine when freeze-dried. Helenine is partially inactivated by exposure for 3 minutes to the temperature of a boiling water bath and is completely inactivated by autoclaving at 15 pounds' pressure for 15 minutes.

The data presented suggest that helenine acts, either directly or by triggering some mechanism of the host itself, to destroy virus by a process which renders the latter non-antigenic. This effect may be exerted by action upon the virus itself or by interference with some stage in the developmental cycle of the virus.

While the chemical nature of helenine is not known, the presence of a large proportion of polysaccharide in crude active preparations might suggest the possible importance of this class of substance in helenine activity. It is believed that helenine differs from the polysaccharide reported by Horsfall and McCarty and the penicillin impurity reported by Groupé and Rake to be active against certain viruses. It may be related, however, to the antiviral substance recently reported by Powell and his co-workers.

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