1. Studies on a large number of tissues obtained from fatal cases of human poliomyelitis have revealed that the virus is distributed predominantly in two systems: (a) certain regions of the nervous system, and (b) the alimentary tract.
2. Poliomyelitis virus was demonstrated in the walls of the pharynx, ileum, and only once in those of the descending colon, while the contents of the descending colon regularly contained the virus.
3. The presence of virus in the walls of the alimentary tract appears to be the result neither of generalized dissemination of the virus nor of secondary centrifugal spread, but rather that of primary localization or portal of entry.
4. In the absence of evidence of any demonstrable centrifugal spread to peripheral collections of nerve cells (e.g., in the superior cervical sympathetic ganglia, suprarenals, salivary glands), the presence of virus in the abdominal sympathetic plexus of one case may be indicative of at least one pathway of centripetal virus progression.
5. The absence of demonstrable virus in the nasal mucosa, olfactory bulbs, and anterior perforated substance suggests that neither the upper respiratory tract nor the olfactory pathway were affected in the cases of human poliomyelitis studied in the present investigation.