302                      Pasteurellosis in White Mice

         Details of other strains used for comparative tests.

                              PATHOGENICITY

Primary cultures were pathogenic for guinea-pigs, rabbits and mice, death
occurring in about one to four days. On sub-culture the organism gradually
lost its virulence. In fact, a rabbit that was inoculated with 0.5 c.c. of a
saline emulsion of 24-hour blood agar culture of the organism that had
undergone subculturing for about six months, did not show any disturbance
in health or condition. It was destroyed after about a month to see whether
any pseudotuberculous lesions were present, but no evidence of such lesion
could be detected.

                        AGGLUTINATION REACTION

Although the organism manifested the characters common to the pasteur-
ella group, yet its definite type could not be determined. Hence serological
tests were undertaken. Homologous serum was prepared by inoculating a
rabbit (No. 99) with carbolised saline emulsion of the culture in four successive
doses :—0.25 c.c., 0.5 c.c., 1.0 c.c. and 1.5 c.c. A week after the last injection
the rabbit was bled and the serum separated and stored.

It is necessary to state here a special feature relating to the preparation
of the antigen. Much difficulty was experienced in the preparation as the
growth could not be emulsified in the usual way. In spite of vigorous shaking,
there was always a tendency for the culture to remain flocullar or in strands,
unmixed with the solution. Many trials were made to obtain a uniform homo-
genous emulsion without success. This disturbing factor was overcome by
the following methods :—

The organism was sown on serum agar as the growth appeared more
abundant and less adherent. After 24 hours incubation, a little quantity