One day in June, 1900, J. experienced a feeling of discomfort in the articulation of the lower jaw--the sequel, as a matter of fact, to a slight alveolo-dental periostitis in the neighbourhood of a bad tooth--and, interpreting the sensation as a new and grave symptom in the march of his malady, forthwith proceeded to investigate its development by playing with his maxilla. Then ensued a perfect debauch of masticatory movements, in which agreeable repetition of every conceivable grimace was joined to protrusion and retraction of the jaw in the search after articular cracks. He became so wholly preoccupied with this tic of mastication that ere long he had begun to pinch the mucous membrane on the inside of the right cheek between the hindmost molars, and this fresh object of absorbing attention in its turn led quickly to some excoriation of the mucosa on both sides. No halt was called by the lower jaw to give the abrasions time for repair, with the natural outcome that they suppurated and paved the way for an attack of infective stomatitis with pain, fever, and malaise, which necessitated the application of the thermo-cautery to the ulcerated areas for its relief. The explanation given by the patient of the evolution of the process was controlled by interrogation of the parents, and no doubt was left as to its genuineness. In the attempt to dispel the articular discomfort, he had accidentally bitten himself, but the consequent pain did not deter him from repeating and continuing the act until its execution was irresistible. In these and similar cases, the infelicitous rehearsal of the movements of mastication is practically always associated with an imperative desire to experience a sensation at the place actually bitten. _Cheilophagic_ children, who bite their lips unceasingly, usually commence by nibbling at some half-separated fragment of epithelium on the edge of a labial fissure, with the inevitable result that the erosion is enlarged and fresh particles of the mucous membrane are detached. Youthful candidates for tics can scarce escape from the vicious circle. A juvenile patient of ours, F., was in the habit of gnawing so vehemently at the most insignificant little irregularity of the mucosa that his lips were constantly chapped and bleeding, and as they were no less constantly being moistened by saliva, a succession of new cracks made their appearance, to be promptly torn apart by the teeth. Local applications of nauseous substances are not always sufficient to discourage these young "cheilophagics." It is still more frequent to meet with _onychophagia_, a condition rightly held to be a stigma of degeneration, and acknowledging the same pathogenic mechanism as all biting tics.