204          Studies on a Natural Outbreak of Pigeon-Pox

                    FILTRATION EXPERIMENTS

One per cent saline emulsion of the cutaneous crusts after autolysis at
37°C. for one hour and centrifugation was filtered through an unused Berke-
feld 'V' candle and Pasteurella avisepticus was added to the virus emulsion
before filtration to control the safety and efficacy of the filter. The
filtration was done under negative pressure at 56 cm. of mercury and it took
about thirty minutes to deliver about 25 c.c. of the filtrate. The filtrate, as ob-
tained above, was tested for bacterial sterility and was found to be sterile.
It was swabbed over the feather follicles of five healthy pigeons (Table III).
Five more pigeons were then inoculated with the unfiltered emulsion to serve
as controls. Four out of the five pigeons inoculated with the filtrate reacted
typically and in one, Pigeon No. 38, there was no reaction. Out of the five
control pigeons, inoculated with the unfiltered material, four reacted and one
was found to be resistant.

                                TABLE III

                        Filtration experiments

                    CROSS IMMUNITY TESTS

(a) Testing the immunity of pigeons, immunized with the English strain of
pigeon-pox virus, against the Indian strain of the same virus.—Five pigeons
immune to the English strain of pigeon-pox virus were tested with the Indian