J. F. SHIRLAW AND P. R. KRISHNA IYER 203
Test animals of each batch were given subcutaneously at the point of the shoulder a flat dose of
2 c.c. of the respective vaccine and the majority reinforced with the original vaccine, stored at 5ºC.
between the intervals of vaccination which varied from one to three months. Animals were tested
at varying intervals after vaccination and the results are given in Table I. The test that we have
employed has given clear-cut results. Thus, when an animal has been successfully immunized it
can withstand a very considerable dose of fully virulent virus. Further, failures in immunity tests
are decisive, and partial or incomplete immunity indicated, we consider, by arrest and healing of
the local lesion. In the Assam batch, vaccination was reactionless, except in one animal which died
of pleuropneumonia eight days after the reinforcing dose or 76 days after the first vaccina-
tion; signs of disease were seen in this case 64 days after the first vaccination. Of three
animals tested for immunity with the homologous virus, one animal alone proved immune; the
interval between initial vaccination and test was 278 days. In two animals which succumbed to
the test dose this interval was 84 and 92 days respectively. Both these animals showed
an acute generalization of disease indicating a complete absence of immunity. Of the two
animals of this batch tested with Australian 264 lymph virus, one showed no evidence of immunity,
whilst the other was partially immune, but it is to be noted that the two controls used in this test,
one for each animal under test, reacted in the same way. In the second batch of cattle vaccinated
with Australian 264 culture vaccine and tested with homologous virulent virus, one animal tested
288 days after the first vaccination reacted severely and died with acute generalization of the disease.
One animal tested at 258 days survived a severe reaction. The control to each animal tested re-
acted fatally. It will be noted that, of the three animals vaccinated with the 63rd generation
Australian 264 culture, two reacted fatally, thus proving this generation unsafe in the cattle used,
yet, ten generations later, this culture seemed to have little protective capacity against the homologous
virus. Three animals of the same batch tested with Assam lymph virus at 187, 164 and 164 days
were proved immune, the controls reacting fatally. Thus, it appears that the 73rd generation
Australian culture protects feebly against Australian 264 virus, but adequately against the Assam
virus. It is equally possible, on these results, that the Australian 264 virus is more potent than the
Assam virus. It may also be noted that the interval elapsing between initial vaccination and test
of animals with the Assam virus was considerably shorter than in animals tested with Australian
264 virus. In immunity tests of all animals of this batch, however, the interval between vaccina-
tion and test was sufficient to ensure a maximum development of immunity.
It is stated by Bennett [1932] and other workers that as good an immunity can be established
with one dose of properly selected culture vaccine as with two suitably spaced doses, and this principle
was followed in the vaccination of the third batch of cattle with 72nd generation Australian 173
culture vaccine. Two animals tested with virulent Assam lymph virus 189 and 305 days after
vaccination were immune while the controls reacted fatally. However, a mild but definite reaction
to the test dose was seen in the 2nd animal which would appear to indicate, that the 72nd generation
of the Australian 173 culture vaccine was not so fully protective against the Assam virus as the 73rd
generation of the Australian 264 culture vaccine; the reaction to immunity test of the 1st animal
of the batch also indicates that the 72nd generation of the Australian 173 culture vaccine protects
very little against Australian 264 lymph virus.
In animals vaccinated with the Kenya strains, protection is afforded against the Assam virus,
and feebly against the Australian 264 virus, which seems further to indicate that the Assam virus
is weaker than the Australian 264. The results in the last batch of animals vaccinated with the
Rhodesian R strain culture vaccine indicate that the immunizing value is poor or, alternatively,
that there is little immunological relationship between this strain and the Assam. This point could
only be settled by the reverse test, i.e. vaccination with the Assam strain and testing with Rhodesian
R virus which was not, of course, available. The same remark applies to all tests of the Kenya
culture vaccines. Although the number of animals used in the tests was necessarily limited, the
presumptive evidence is that the Assam virus is immunologically related to the Australian and Kenya
strains and doubtfully to the Rhodesian strain. Although the results in general indicate that the
Australian 264 virus is a stronger virus than the Assam, it is equally possible that a quantitative