This report deals chiefly with a study of the nature of fowl-pest virus and several observations on this subject,
The results obtained can be summarized as follows:
1. The successive passage of the fowl-pest virus through pi-geons caused the possibility of enhancing it and any distinction with regard to susceptibility due to age of the pigeon has no longer been demonstrated as described in the previous publication.
2. The period which elapsed between injection and death did vary, but became shorter, near the 100th passage, the period of16 N. NAKAMUSA and Y. KAWAMURAincubation being shortened within 4-5 days and the death being resulted within 24 hours after the appearance of the symptom.
3. With regard to the distribution of the virus in the diseased pigeon, it may be conclusively demonstrated that the affinity of the virus to the brain tissue will be enforced in parallel to the generat-ion of transmissions, but the distinct fall regarding its presence in other organs, above all in the liver tissue, being observed. More-over, there was not any difference in the susceptibility among the infected pigeons which received several injections of brain-virus from a higher dilution, i.e., 1:1, 000, 000 to a lower dilution, i.e., 1:10, the course of disease being almost constant.
4. So far as the present generation concerned, the brain-virus passed through many pigeons was always fatal to fowls and such enhanced virus did not show any decrease by the successive passage through fowls or by the alternate passage through pigeons and fowls, but some increase in virulence happened to be resulted.
5. Regarding the symptoms manifested by the affected birds in the use of such enhanced brain-virus, the remarkable nervous disturbance followed by a sudden appearance of coma was generally observed and in such cases the characteristic haemorrhagic findings on the mucous and serous membrances were scarcely demonstrated at autopsy.

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