The comparative growth rates of a virulent (CG 179) and an avirulent (B) strain of NDV in the chicken were analyzed. Following intramuscular inoculation, the CG 179 and B strains both increased at the same rate in the extraneural tissues, i.e. the blood, lung, rectum, and spleen, but the CG 179 strain showed an accelerated growth rate in the brain.

The CG 179 strain also multiplied more rapidly in the brain than the B strain following intracerebral administration of minimal inocula.

Recovery with the B strain was associated with a decline in virus titer, first in the circulating blood, then in the visceral organs, and lastly in the central nervous system.

Certain neuropathological observations were correlated with the pattern of virus growth.

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