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Bovine Pleuropneumonia
but not qualitative, immunological variation exists. To determine this point, cross immunity tests
in cattle immunized with greater certainty against both strains would be necessary and the next
test is so framed.
Vaccination of cattle by 'tail-tip' method with Australian 264 and Assam culture vaccines and cross
immunity test. Four cattle were vaccinated tail tip with 0.5 c.c. 7th generation Assam culture and
reinforced tail-tip twenty-six days later with 1 c.c. 8th generation of the same culture. The vaccina-
tion was reactionless. One month after the second vaccination these animals were tested with 5
c.c. virulent Australian 264 virus, and no reaction ensured, whilst one control to the test reacted
fatally. Similarly, four cattle were vaccinated with 7th and 8th generation Australian 264 culture.
On test with 5 c.c. virulent Assam virus one month after the reinforcing dose, two cattle reacted as
severely as the control to the test. Evidence of immunity in the other two animals was slight, both
showing a severe reaction with eventual recovery. The results indicate that cattle fully immunized
against the Assam virus are solidly immune to the Australian 264 virus and that cattle immunized
with Australian 264 vaccine acquire only a feeble immunity against the Assam virus. This seems
to contradict the previous results with attenuated culture vaccine, in which it appeared that Australian
264 culture vaccine adequately protects against the Assam virus. This discrepancy in results cannot
be explained, but we attach more importance to the results of the latter test and consider it probable
that a more substantial immunity is conferred by a highly virulent culture than by a definitely
attenuated culture. Whatever be the explanation, the result of the test indicates some doubt in
the immunological relationship of Australian 264 and Assam viruses.
THE SEROLOGICAL REACTION OF HILL CATTLE VACCINATED WITH AFRICAN, AUSTRAL
VIRUSES-AGGLUTINATION TEST
The limited number of tests performed was intended to give some idea of the serological rela-
tionship of the strains of viruses under study and the correlation on the basis of immunity tests.
Some divergence of opinion exists on the uniform presence of agglutinins in the sera of animals ex-
posed either to natural or artificial infection, and opinion is divided on the question whether the
agglutination test is of practical value in the detection of infected animals or as an indication of the
degree of immunity following vaccination.
Walker [1922] found that the percentage of error in the test was considerable. Heslop [1920]
and Kearney [1923] believed the test to be of real practical value. Dahmen [1924] was doubtful
of its value and favoured a combined agglutination-precipitin test. In the experience of Nakamura,
Futamuru and Watenuki [1926] 46 per cent of the sera from known positive cases of the disease
gave negative results, and conversely, 30 per cent of healthy sera were positive to the test. Ito,
Yamagive and Itabeshi [1930] concluded that the test does not give as clear-cut results as seen
in many bacterial infections, the maximum titres being around 1/80 with positive results not ex-
ceptional in healthy animals. Daubney [1935] found serological tests unsatisfactory in detecting
carriers in animals exposed to infection. In a critical analysis of the test, Campbell [1938] considers
that results depend on the antigen used, and claims good results for a 0.2 per cent formalinised
antigen adjusted to a No. 2 Brown opacity tube.
In our tests, two types of antigen have been used. The first was a 0.5 per cent carbol saline
suspension of a ten-day serum broth culture centrifuged at 12,000 revolutions for 40 minutes. The
collected deposit of each run was adjusted to a No. 2 Brown opacity tube, one litre of culture yielding
about 20 c.c. antigen. The second antigen used was prepared according to the formula of Campbell
[1938]. With carbolized antigen prepared from Assam and Australian 264 cultures, the sera of
cattle vaccinated against Assam, Australian and African viruses (Table I ) were tested with,
in addition, the serum of an animal that had survived the intravenous inoculation of virulent
Assam lymph virus and later proved immune (animal 12, Table II). In this batch, the test was
carried out one month after the first vaccination and the results are given in Table II. Readings
were made after 2 hours at 55ºC. and again after the tubes had stood at 37º.5 C. for 24 and 48 hours.
Agglutination was usually indefinite at two hours and complete at the 24th hour with no variation
in titre at the 48th hour. The results of the second test, using formalinised antigen, are given in