S.
GANAPATHY
IYER
17
by Burnet [1936], show patchy ectodermal proliferation, followed by, or
associated with, gross vacuolation of the epithelial cells and necrotic changes
(Plate IV, figs. 4, 5 and 6). In some of the vacuoles of the proliferating
ectodermal cells there is evidence of acidophilic bodies, which Burnet [1936]
considers as droplets of mucin (Plate IV, fig. 6).
Lesions. Eggs in which the embryos had died but in which no lesions
were found, invariably contained the active virus. The characteristic lesions
of Newcastle disease in eggs were observed in almost all the eggs in the differ-
ent passages (Plate IV, fig. 1). Serial cultivation of the virus through eggs
was successfully carried out. The virus continued to be lethal for the embryo
and took a generalized form of infection. The virus was confined not only to
the membrane, but also present in the embryo. The death of the embryo
was seldom prolonged beyond the third day following inoculation.
(i) Experimental vaccination of fowls with egg virus. Susceptible fowls
were inoculated with the egg cultivated virus at different passages. The virus
had maintained its normal virulence for fowls up to the 19th passage in one
line and to the 12th passage in the other. But when the 1st line egg virus,
after having undergone 33 passages, was inoculated into healthy fowls, there
were indications that the virus had undergone some modification and was
admirably suited for the immunological work in the form of what may be
termed ' live-virus-vaccine '. Attenuation of the virus in the 2nd line, how-
ever, was evident at the 14th passage. From Table IV, it will be seen
that fowls have been successfully immunized against Newcastle virus by em-
ploying the egg technique. The immunity was satisfactory in the different
tests after the egg virus had undergone 33 passages with Line I and 14 passages
with Line II. Fowls, inoculated with the vaccine, seldom showed any sign
of illness but, rather, appeared to have acquired absolute protection against
what may be considered as severe infection. At the time of writing, 57
passages, during 12 months, have been made with the 1st line of the virus.
The virus still kills the embryos two to three days after the inoculation
but is not lethal for fowls. It is, therefore, invaluable as an immunizing
agent; moreover, there has been no difference in the ' takes' in the
different passages.
It is, however, realized that the various factors, that would influence the
successful employment of this method for prophylaxis against Newcastle
disease on any large scale, still remain to be investigated. While evidence
has been adduced to show that Newcastle disease virus, after being cultured
through developing chick embryos, has become so attenuated as to enable it
to be employed as a safe immunizing agent, the work of Smith, Penna and
Paoliello [1938], on yellow fever vaccination with cultured virus may be re-
viewed here, for the behaviour of the two viruses is more or less identical.
Vaccine for human use against yellow fever was prepared from the develop-
ing chick embryos inoculated with the culture-virus. In making the vaccine,
only virus which had been cultivated through from 205 to 287 passages was
used. Eggs with living embryos about seven days old were selected for inocu¬
lation After inoculation the eggs were incubated at 37°C. for three or four
days and then the embryos were taken out for vaccine preparation. A 10
per cent suspension of the finely ground tissue in normal human serum was