194
Protective Inoculation with Dry Pigeon-Pox
parts of the world, has now almost been completely discarded and constitutes no more than an item of
historical interest in literature on the subject, its serious drawback being, as is well known, that it
sets up dangerous foci for spread of the disease owing to the severe reaction occurring in the inoculated
animals. Similar remarks apply to the Borrel method [1930] which held the ground for many,
years before the introduction of sensitised vaccine, for, as remarked by Bridré and Boquet [1933],
the virus employed in this method ' is not a vaccine; its inoculation engenders sheep pox transmis-
sible by simple contact and the lesion, even if unique, is a source of active virus'. Blane and Martin
[1937] obtained inconstant results with the Borrel method in Morocean sheep when the latter were
used as donors of the anti-serum required for use in this method. In India, Srikantiah [1936], states
that he has employed the method successfully in 233 sheep. He, however, refers to the failure of
its use by another worker in Madras during 1929-1930. Later, Srikantiah used what he designated
the 'cutaneous method' of preparing sheep-pox vaccine: the infective material was applied on the
scarified portion of the skin of a healthy sheep and the epithelial layers of the resultant pustules were
removed by scraping from the 13th to the 16th day. Two cubic centimetres of 1:3 glycerine solu-
tion was added to every gramme of the scrapings and the mixture preserved in cold storage, one part
of the vaccine being diluted with two parts of saline at the time of despatch for field use. It would
appear that two flocks out of three in which the vaccine was tested did not show any reaction and
that eight of the sheep died; this being ascribed to some unknown accident having occurred to the
vaccine. It has, however, been observed by the present writer that pustules which are formed after
four or five days contain the maximum amount of virus and that, as will be seen from what has to
be stated later, vaccine in wet suspension, even when preserved in cold storage, quickly loses its
potency. It is more than probable that these factors contributed wholly or partially to the failure
to obtain successful results by the 'cautaneous method'.
The position in regard to protective inoculation against fowl-pox is more satisfactory, this being
doubtless due to the widespread nature of the disease and the consequent availability of morbid
material for experimentation, as also the obvious fact that birds are simpler and less expensive to
experiment with. Of the more noticeable advances in this field, mention may be made of the intro-
duction of pigeon-pox virus for use in fowls and of the so called 'stick method' of vaccination.
Reference may also be made to the findings made by Beller [1931] on the specific nature of fowl-pox
lesions as distinguished from those due to deficiency of vitamin A. It is also noteworthy that,
contrary to the generally accepted view, Kliger and Aschner [1931] have stated that fowl-pox and
avian diptheria represent distinct disease entities, so that recovery from one does not confer protec-
tion against the other. If this statement is correct, then the percentage of success obtained with
pigeon-pox virus against fowl-pox must have been substantially higher than what has been claimed
for it in the past. It should, however, be mentioned that the relative value of fowl-pox and pigeon-
pox virus still continues to be a subject of controversy. While, a priori, it would seem problematical
whether a substantial degree of immunity is obtainable from the use of a heterologous vaccine,
the actual experience of most workers points to a contrary conclusion. Thus James [1931], Glover
[1931], Johnson [1932], Bierbaum [1935], Doyle [1935] and others refer to the highly satisfactory
results obtained by them from its use, while, as will be seen from what has to be stated later, the
present writer found it consistently effective in the experimental inoculation of fowls against pox.
Michael [1932], Brunett [1933], and Lubbehusen and Ehlers [1934], record having found pigeon-pox
virus to be of little value in protecting fowls, but as remarked by a number of later workers, their
failures were in all probability due to faulty technique either in the preparation or in the application
of the vaccine. It appears, however, generally agreed that the immunizing value of fowl-pox virus
per se is superior to that of pigeon-pox virus, but that the use of the former is followed by a severe
and sometimes fatal reaction, whilst egg production may be suspended altogether [James, loc. cit.];
Graham and Barger, 1936, Stafseth, [1931]. The danger of using fowl-pox virus is strikingly illus-
trated by an instance cited by Leyhausen [1933] in which considerable mortality occurred in a flock
of chicks inoculated with a proprietary pigeon-pox vaccine containing traces of fowl-pox virus whilst
no untoward symptoms occurred in birds which received pigeon-pox vaccine alone supplied at the
same time by the same firm. The use of fowl-pox virus would thus appear to be fraught with real