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Bovine Pleuropneumonia
p.i. The test dose varied between 0.1 c.c.—2 c.c. One of the ten animals vaccinated with 2 c.c.
refrigerated lymph virus and both controls reacted severely and were destroyed and the remaining
twelve animals under test showed no reaction and were solidly immune.
Vaccination with lymph virus stored at room temperature, 13—24°C. Previous results gave an
indication that a measure of immunity might be established with suitable doses of a fully potent
virus allowed to attenuate at room temperature (13°—24°C). It was considered that attenuation
for one month or slightly longer would ensure safety and yet evoke a reaction sufficient to indicate
the degree of diminished virulence and possibly the degree of immunity to be expected. Two cattle
were inoculated subcutaneously at the point of the shoulder with 2 c.c. Assam 1 lymph virus stored
at room temperature for one month and four cattle were similarly inoculated with the same virus
stored at the same temperature for a further six days. No reaction occurred in any of the animals
tested; two animals of the second lot vaccinated died of bovine encephalomyelitis accidentally
contracted from experimental cattle housed some little distance away, thus leaving two animals of
each lot vaccinated available for immunity test. All four animals were tested, along with two controls,
forty-one days after vaccination. The vaccinated animals reacted as severely as the controls and
all died.
Vaccination with dried and heat-treated muscle vaccine. Thin strips of muscle from the local
lesion of a routine virus producer were dried in vacuo over anhydrous calcium chloride and then
powdered in a mortar, the entire process taking six days. The virulance of this preparation was
tested in a hill bull, which, tested at the point of the shoulder with 5 c.c. saline suspension, reacted
fatally. The vaccine was prepared as follows : the powder was made into a thick paste with normal
saline and divided in two parts. One part was heated at 70°C. for two hours and the other at 55°C.
for two days. Four cattle were used in the test of the vaccine; two were subcutaneously inoculated
with 1 cgm. and 5 cgm. respectively of the 70°C. heated vaccine and a month later given a reinforcing
dose of 10 and 50 cgm. respectively of the same vaccine stored meanwhile at 5°C. The other two
cattle were inoculated in the same way and at the same dose rate with 55°C. heated vaccine. No
reaction ensued in any of the animals so vaccinated and all were tested for immunity, with one
control 65 days after the first vaccination, the test dose being 0.5 c.c. homologous virus. No reaction
resulted in the four animals under test and the control reacted fatally, thus indicating a substantial
measure of immunity. This test proved so encouraging that a second test of the method, with some
modification, was carried out. The muscle powder paste was heated at a lower temperature for a
much shorter period (50°C. for 2 hours) in this way hoping to obtain a less attenuated and
therefore more potent vaccine. A preliminary test of this vaccine showed it to be safe. One hill
bull was tested at the point of the shoulder with 10 cgm. of the freshly prepared vaccine and no re-
action developed within 12 days during which time the vaccine was stored at 5°C. Five cattle
were then used in the test of the vaccine, each animal receiving 10 cgm. subcutaneously at the point
of the shoulder; two were reinforced with 20 cgm. 16 days and two with 50 cgm. 20 days
after the first vaccination, the same vaccine maintained at 5°C. being used. The fifth animal of
this batch was not given a reinforcing dose. All six animals, including that used in the safety test
of the vaccine, were tested for immunity along with one control. The animal used in the safety
test was 63 days p.i. and the main batch was 51 days p.i. The test dose was 0.5 c.c. homologous
virus subcutaneously at the point of the shoulder. Four animals of the main batch and the control
reacted severely and died. The fifth animal, one that had been given a reinforcing dose of the vaccine
reacted strongly but eventually recovered. The immunity test was, therefore, a failure with the
exception of the animal used in the preliminary test of the vaccine. The virus used in the preparation
of the vaccine was fully potent as a hill-bull subcutaneously inoculated at the point of the shoulder
with this virus, one day after its selection for the vaccine, reacted fatally. A possible explanation of
this failure is that some deterioration of the vaccine occurred during the 12 days storage at 5°C. The
method seems to hold out possibilities that would have been further explored had not experiments
in immunity along other lines gained a large measure of success, notably tail-tip vaccination with
fully virulent culture virus.