(2) After subjecting the sulcus to interference, its histological appearance is compared with that of definite parodontal disease.

(3) Various methods were adopted for these experiments, which were performed on monkeys.

(4) Artificial pockets were produced by detaching the subgingival epithelium and underlying connective tissue from the cementum. Results: (a) Cementum is easily removed accidentally, when scraping monkeys' teeth. (b) Reattachment of connective tissues to cementum is effected, but is usually incomplete. (c) Epithelium always firmly reunites with cementum. (d) The artificial sulcus which is usually deeper than normal does not show, microscopically, the same pathological changes as in parodontal disease.

(5) In other experiments, in addition to deepening the sulcus, the cementum lining the pockets was also removed, leaving denuded dentine in contact with the connective tissue. A similar condition was achieved by another method in which a dental bur was inserted between two teeth below the gum margin.

Results: (a) The gingival epithelium is capable of forming a weak attachment to the dentine, though this does not usually occur. It always proliferates down and unites with the nearest layer of cementum. It seems to have a peculiar affinity for this tissue. (b) Underlying connective tissue does not usually unite with the dentine. When this happens it is effected by the regeneration of cementum, this new tissue being lined by new cementoblasts. (c) The width of the periodontal membrane, which was increased by the experiment, is reduced to a more normal level by deposition of new alveolar bone, and to a lesser extent by regeneration of cementum. (d) In this series of experiments the artificial pocket is permanent and somewhat resembles that of parodontal disease. This is probably due, not so much to the injury, but to its effects creating a space which forms an area of chronic stagnation.