In the preceding article1 a method was described of preparing colonic explants in dogs and of quantitating the secretion of mucus by such explants. On the days immediately after the preparation of the explants, ulcers were found near the center of the grafts. A feature constantly associated with this phenomenon was marked muscular spasm of the explants. When dressings were continuously used the initial muscular spasm disappeared, the ulcers healed and the grafts retained indefinitely a normal gross and microscopic appearance. Thereafter, mucus was secreted largely in response to the initial mechanical stimulation of the dressings, and this secretion was associated with muscular contraction.
It was noted that chronic surface irritation produced by leaving the grafts without dressings for forty-eight hours led to muscular spasm and an initial copious outpouring of mucus. This was soon replaced by a more watery secretion, at a time when microscopic study of the