Local passive immunity against anthrax infection.

Owing to the varying results obtained in our previous work in which we used guinea pigs as the test animal, the following experiment was carried out on rabbits. Anti-anthrax serum from Mulford & Co. was used with normal horse serum as control.

Ten control rabbits were prepared with normal horse serum: 2 intravenously, 4 subcutaneously, and 4 intradermally; each animal receiving 3 cc. Ten other animals were given anti-anthrax serum by the same routes and in the same dosage.

Thirty hours after the serum injection the resistance of each animal was tested by intradermal inoculation. The rabbits prepared by intravenous injection of the serum were inoculated intradermally over the abdomen. The rabbits prepared subcutaneously or intradermally were inoculated intradermally either at the same point or on the opposite side.

Two to four fatal doses of Bacillus anthracis were given. Previous titration of this culture showed that 1/5000 of a 24 hr. agar slant was consistently fatal for rabbits weighing from 1500 to 2500 grams. Two control rabbits, having received no previous treatment of serum, were inoculated intradermally with one and two fatal doses respectively.

Of all the animals prepared with normal horse serum only one survived. This rabbit had been prepared intradermally and later received two fatal doses in the same region.

Both of the animals prepared by intravenous injection of antianthrax serum died. Of the four animals prepared by subcutaneous injection of the anti-anthrax serum, one survived. This rabbit had received two fatal doses in the same region as the previous subcutaneous injection of serum.