PEEIOSTOTOMY. 291 



which may be kept in place by securing it to the halter of the 

 patient, to prevent it from falling into the sinus. 



The cicatrization of the wound made by the trephining in- 

 strument springs from the rapid development of granualations 

 which soon fill up the opening. These granulations soon undergo 

 the various changes which take place in the process of calcification 

 and ossification, and the loss of bony substance is soon completely 

 repaired. 



In a few instances, however, the seat of the operation, after a 

 few days, assumes a most unfavorable aspect, becoming swollen 

 and offensive, and betraying the characteristic necrotic odor. In 

 many instances the seat of the necrosis is found to be the edge of 

 the opening, and is due to the imperfect appUcation of the tre- 

 phine, and the destruction of the periosteum. Care must then be 

 taken to remove all the loose necrotic fragments. To allow them 

 to remain imbedded in the granulations and under the sldn, will 

 be to incur the certain hazard of the development of abscesses 

 and the formation of fistulous tracts, which will refuse to heal 

 until the last particle of diseased bone has been exfoliated and 

 removed. 



PERIOSTOTOMY. 



Periostotomy is an operation which consists in the subcutaneous 

 division of the periosteum, on the surface of bony growths. It 

 may be for the purpose of stimulating their resolution, or it may 

 be to relieve the pain arising from the tension of the inelastic 

 membrane as it is pressed upon by a tumor of the bone growing 

 under it. The operation was originally performed by Professor 

 Sewell of the Royal Veterinary College in 1846, and was at first 

 considered to be one of the neatest and most scientific among the 

 methods practiced for the reUef of the lameness due to exostoses. 

 It was considered by Sewell himself to be far superior to any 

 other means then in use, counter irritations, firing, and the rest. 

 But although earnestly supported by the authority of its inventor, 

 periostotomy has not sustained its claims by exhibiting all the 

 results which were promised for it, and experience has shown that 

 it is in many instances not only a useless, but even a dangerous 

 operation. Several special instruments are necessary in its per- 

 formance. These are a peculiar ro%oel scissors (Fig. 306) to incise 

 the skin, for which, however, a special bistoury (Fig. 307) is 



