Suppuration in the socket may be due to a lowered vitality of the tissue, produced by some such local causes as acute or chronic inflammation, and is especially well seen in cases of extraction for the relief of periodontitis, or where the operation has been performed in patients suffering from general debility, syphilis, struma or in fact any of those systemic diseases which tend to lower the vitality of the organism. (4) _Extensive laceration of the hard and soft tissues_ in the neighbourhood of the socket; and (5) _Necrosis of the socket of the tooth_ are also fruitful sources of pain following tooth extraction. (6) _The presence in the wound of a foreign body._--A curious example of this came under notice a few years ago. A patient applied for the extraction of the left first permanent molar. During the operation a portion of one of the cusps disappeared; a search was made for it but, as it was not found, the natural supposition was that it had been removed in rinsing the mouth. The patient for the next three weeks complained of slight pain in the socket for which remedies were tried but proved of little use. Eventually the patient discovered the cusp on the top of the granulation tissue which had filled up the socket. In another case of the same character which came under notice, the offending material was a piece of an amalgam filling. A fractured blade of forceps may likewise act as the offending body. (7) _Injury to the nerve._--Direct injury to the trunk of the nerve is more likely to occur during extraction of the lower third molar than with any other tooth. It is more than probable that many obscure cases of pain following tooth extraction are due to exposure and irritation of the nerve at the apex of the socket. An interesting case of this character was lately reported by Mr. Storer Bennett.[17] The patient, a lady æt. 23, had had the third upper molar dislocated through the use of a Wood’s gag, and, as it was considered hopeless to restore the dislocated tooth, it was extracted without difficulty. The socket in spite of treatment remained painful for the next twelve days, but in the meanwhile granulated healthily, except at its apex, where by the aid of a mirror and probe a spot about the size of a pin’s head was noticed which caused the greatest agony on being touched. Incision of the nerve produced permanent relief. _Treatment._--The treatment naturally depends very much upon the cause. A thorough examination of the socket should be made with probe and mirror. When due to incomplete extraction, another attempt, if considered advisable, may be made to remove the tooth. This proving unsuccessful, the socket should be swabbed with an anodyne drug and, if there is an exposed pulp in the remaining portion of the tooth, the pulp should be touched with fuming nitric acid or strong carbolic acid. The patient should also be advised to use some poppy head fomentation.[18]