In a comparative study of different Salmonella enteritidis phage type 4 isolates we found that those isolates with enhanced heat tolerance also survived better than isolates that were heat sensitive either at pH 2.6, in 10 mM H 2 O 2 , or on surfaces. Culture to the stationary phase increased the heat tolerance of all isolates and the acid and H 2 O 2 tolerance of heat-tolerant isolates. With heat-sensitive isolates, however, extended culture had no impact on survival in H 2 O 2 and only a marginal impact on acid tolerance. The growth phase had no appreciable impact on the surface survival of any of the isolates.

509fers on control media, passages through normal mice and storage at 4°C partially or completely restored the bacitracin sensitivity to all resistant variants. 4. Mouse virulence was decreased in 7 of 9 strains. I t was restored in 6 of the 7 strains by subsequent passages in normal mice. 5. Group specificity was lost in 3 of 7 group B strains aflter induced resistance. 6 . Growth on sub-inhibitory con-centrations of bacitracin stimulated transient conversion from beta to alpha hemolysis in most strains studied. 7. The streptolysin "S" titre was decreased in 2 of 3 resistant variants. Ribo-and desoxyribonuclease activity and the proteinase-streptokinase ratios remained unchanged after acquired resistance.

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Summary A variety of compounds containing a terminal α-ketoaldehyde or α-hydroxyaldehyde grouping showed marked activity against influenza A (PR-8) and Newcastle disease (NJ-KD) viruses in embryonated eggs. One of these compounds, β-ethoxy-α-ketobutyraldehyde hydrate (Kethoxal) appeared to be at least as active as any of the other compounds and the following results were obtained in detailed studies with this compound: Kethoxal was active in eggs when given 24 hr before experimental infection or 6 hr after infection with NJ-KD virus.Kethoxal at the maximum tolerated dose was able to protect eggs against as much as 4 × 106 LD50 of NJ-KD virus, and as little as 24 μg of Kethoxal were effective against low levels of virus.Kethoxal in eggs was active also against vaccinia virus, the GB strain of Newcastle, the London strain, of influenza A′, and against mumps virus.Kethoxal was a potent inactivating agent in vitro against NJ-KD and PR-8 viruses.The probable mode of antiviral activity in eggs was concluded to be through a direct virucidal action on extracellular virus.

The ERA strain of rabies virus was adapted to growth on monolayers of a porcine kidney cell line (PK-2A). A reproducible plaque assay system was subsequently developed, which appears to be satisfactory for conducting plaque neutralization tests.