108 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ I, II

         A fact of some considerable interest in connection with these natural outbreaks
of the disease is that in many of the reports it is stated that crows were noticed
to be dying in very large numbers in the vicinity of poultry farms when the disease
was raging at the time among poultry upon the farms.

                           ISOLATION OF INFECTIVE MATERIAL.

         Trials with mouth-washings, emulsions of internal organs and with blood from
infected birds soon showed that whilst the first two proved infective when injected
under the skin of healthy fowls, the inoculation of blood in this manner some-
times failed to produce infection. Also, the virus proved capable of passing easily
through fine bacterial filters ( " L 3 " candles fitted to Martin's filtering apparatus).
In the earlier experiments, the infective material used in the artificial production
of the disease consisted entirely of mouth-washings, but latterly it was supplanted
by organ emulsion on account of the ease with which the latter could be kept alive
under laboratory conditions. The preservation of the organ emulsion was carried
out on the lines indicated by Doyle [1927] in his report upon the so-called " New-
castle Disease," use being made for the purpose of a mixture of the main cellular
organs of the body, liver, spleen and kidneys. The organs were removed with
strictly sterile precautions from fowls destroyed at the commencement of the
disease, subjected to a process of desiccation, and stored, without the addition of
any preservative, in a refrigerator at a temperature below 4 degrees Centigrade.
As would appear from the following Table, when stored in this manner the material
proved definitely infective for 125 days, and probably until 169 days, in spite of
the fact that in a few instances it was noticed to have developed contaminating
growths of mould.