1. Prussian blue particles pass rapidly from the surface of the olfactory mucosa and within 2 minutes are found in the tissue spaces, in blood and lymph vessels, in the perineural spaces of the olfactory nerve fibers and in the subarachnoid space and pia-arachnoid membrane.

2. There is great affinity of pigment particles for the olfactory sensory cells.

3. Preliminary treatment of the olfactory mucosa with tannic acid does not alter the speed with which this absorption occurs. It does, however, cause an inflammation of the mucosa and appears to prevent the pigment from entering the olfactory sensory cells.

4. Both pneumococci and S. enteritidis pass through the olfactory mucosa and reach the tissue spaces, the vessels and the subarachnoid space with the same rapidity as the pigment. This can be demonstrated both microscopically and by distribution tests. They invade by passage between the cells of the mucosa and there is no apparent affinity of the organisms for the olfactory sensory cells.

5. Tannic acid treatment of the olfactory mucosa in no way alters this invasion of organisms through the mucosa.

6. The pantropic virus, equine encephalomyelitis, was detected in the forebrain as promptly as were pigment and bacteria; neurotropic viruses, however,—those of St. Louis encephalitis, rabies and louping ill,—were not demonstrated in less than 24 hours.

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