These results are presented in support of our theory that lichen planus is an infection by a specific organism. We also believe that individual susceptibility is an important factor in the production of this disease. THE ORGANISM The organism isolated (figs. 1 to 4) is an anaerobic, nonmotile, nonencapsulated, nonspore-bearing, gram-negative bacillus, varying from about 2.5 to about 3.7 microns in length and from about 0.5 to about 0.7 microns in thickness. It is somewhat polymorphic, and not only grows sparsely but also undergoes granular degeneration, and ceases to grow after a short time on the usual varieties of mediums. Though somewhat polymorphic, it resembles organisms of the colon typhoid type, but on account of its poor growth we have been unable to classify it. The manner of growth is curious, dense clumps of various sizes being found in actively growing cultures, with relatively few individual organisms. There is