S.
GANAPATHY
IYER
21
Immunization tests with crystal violet treated egg virus (Table V)
Experiment I. At the time of the vaccine preparation, the virus had
been cultivated in eggs through 12 generations. The egg virus at the 12th
passage had not been modified in its virulence. Fowl No. 2137 which had
received the vaccine treatment 5 c.c. subcutaneously showed no symptom of
illness ; 39 days after vaccination, it was exposed to coop-contact infection ;
it remained healthy ; but 54 days after vaccination, it was changed to another
coop in which a bird had previously died of experimental disease. The vacci-
nated fowl died, however, six days later. As it showed lesions suggestive of
the disease, animal sub-inoculation was carried out and it was proved that the
bird died of Newcastle virus infection.
Serum-virus neutralization test. Serum from fowl No. 2137 concerned in
the previous experiment was collected on the 14th day following the vaccine-
treatment. To 0.5 c.c. serum was added 0.5 c.c. fowl-passage virus. The
contents were mixed well and incubated for 18 hours at 37°C. Control
tubes containing virus plus normal fowl serum and virus plus saline were
also prepared. The above mixtures were inoculated into fowls which were
apparently healthy. All the fowls died. From this, it was concluded that
the serum from the vaccinated fowl evidently contained no specific neutral-
izing antibody.
Although these results were not very satisfactory, it seemed possible that
with greater attention to the physico-chemical aspects, this kind of vaccine
might be improved.
Experiment II. In this experiment, the vaccine was prepared from the
virus after cultivation through 23 generations in the developing eggs. The
fowls were inoculated with 5 c.c. each under the skin on 29 March 1940.
The birds remained lively and showed no symptoms of the disease. They
were, however, shown to be immune against subsequent experimental
infection. In connection with equine encephalomyelitis, it is stated that
the egg virus treated with formalin confers more rapid protection and may be
used in the presence of virulent outbreaks [Lyon and Wyckoff, 1938] ; [Beard
et al., 1938]. On 16 May 1940, these two fowls were left in a pen along with
a number of experimentally infected fowls and they remained healthy.
The results of this experiment appear very promising and it may be con-
sidered as a successful attempt at vaccination against Newcastle disease.
It is possible that the virus, after cultivation in eggs, has acquired some new
property which has rendered it an efficacious and safe immunizing agent, thus
paving the way for useful line of further research following the modern con-
cept of the chorio-allantoic method of virus-culture. At this stage, it is
recognized, however, that the results of a test conducted with so few birds
cannot be accepted as conclusive. Work on similar lines was, therefore,
repeated in subsequent experiments.
Experiment III. Several points of useful information emerge from this.
From the fact that fowl No. 2276, which was one of the six vaccinated fowls,
died when tested for immunity by experimental inoculation seven days after the
vaccine treatment, and at the same time fowls which were tested for immunity
14 and 21 days following the vaccination remained healthy, it is evident that,
consequent on treatment with the crystal violet vaccine, protection is perhaps