1. When suspended in slightly alkaline (pH 7.4 to 7.8) saline dilutions of clear, hemoglobin-free normal monkey serum, the virus of yellow fever from infected monkeys and from infected, but blood-free, mosquitoes, usually acts as if it were possessed of a positive electrical charge.

2. The virus tends to assume a negative charge in fluids having a slightly acid reaction.

3. The isoelectric point of the virus seems to be in the neighborhood of pH 7.0, possibly ranging from pH 7.3 to pH 6.9.

4. Exposure to fluid having a reaction of pH 5.0 for 3 hours appeared to inactivate the virus.

5. In experiments in which the suspending fluid was prepared with normal serum diluted with distilled water and containing a good quantity of partly hemolyzed erythrocytes, the virus tended to migrate to the anode.

6. The protective bodies in yellow fever immune serum appear to carry a negative charge in slightly alkaline saline dilutions of serum.

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