It may seem incredible to all who read this that a mucus channel or a fistula can be formed for ten, twenty, forty, or more years before the formation of pus takes place in it; and that the pus exerts no part in producing the diameter or length of the fistula, which may have a capacity of six, eight, or more ounces of fluid. As soon as the chronic inflammatory process has penetrated one or more layers of the mucous membrane, mucus channel or fistula-formation must take place. If the sphincter muscles be rather weak or lax I would not expect sacculation of the rectal mucosa to occur to any extent. In these cases, however, the muco-cutaneous channels are usually found quite large and numerous. Of course the extent of the ano-rectal symptoms in each case depend upon how severe the chronic inflammatory process has been, and is, at the lower portion of the enteric canal. Often you will find that the seat of the most active chronic inflammation is in the middle and upper portion of the rectum, involving also the sigmoid colon. In these cases the ano-rectal symptoms are not numerous, if there be any at all, on the mucous membrane, but under it you may expect mucus channels that serve as outlets for the inflammatory product. In every case of chronic proctitis and sigmoiditis submucous and subtegumentary fistulæ can be found, and my experience in tracing them warrants me in stating that periproctitis and perisigmoiditis is present also; the latter pathological condition being due to the invasion of submucous and subtegumentary channels or fistulæ around the outside of the structure of the anus and rectum, extending far up into the neighboring tissues of the pelvic space that support the rectum and sigmoid flexure. The formation of pus in a submucous or subtegumentary channel that has existed for many years does not make it a disease; it is only another incidental phase added to an already existing symptom of chronic proctitis. Mucus fistulæ should be diagnosed and treated early in their formation, or at least before the tissues involved became so deteriorated as to form pus in quantity sufficient to occasion the usual period of suffering, fever, loss of rest and sleep before the pus is freed from its enclosure. The formation of pus in a mucous fistula is only incidental and marks a stage in the distinctive changes that have been going on for many, many years in the tissues involved in the inflammatory exudation.