57

was so weakened as to be unable to kill rabbits and
buffaloes.

Passage through certain species of animals increases the
virulence up to a standard virulence for that species, for
example, Rabbits, Rats and Buffaloes.

This standard virulence is higher for rodents than for
ruminants.

                                IMMUNITY.

Immunity may be conferred on animals against H. S.—

I.    By feeding on virulent bouillon cultures.

II.    By starting with less than a fatal dose of pure
bouillon culture, and giving increasing doses.

III.    By commencing with an inoculation of bacilli
separated from their toxins and later giving toxin subcu-
taneously in increasing doses.

IV.    By inoculating attenuated bacilli.