OSTEOID TUMOURS. 437 



generally of a slow, but sometimes of a rapid growth. They 

 consist of a cancellous bony tissue, forming trabeculse, which 

 surround spaces filled with a greyish white, vascular, fibrous 

 material, in which a sparing quantity of cells and nuclei are 

 imbedded. 



These tumours may vary in their density, from the presence 

 of more or less bony structure in their formation. 



The origin of osteo-sarcoma is very obscure, but it seems to 

 depend upon the tubercular diathesis, as upon dissection the 

 various structures adjoining the tumour are usually found matted 

 together, and firmly adherent to it, whilst spots of tubercular 

 matter may be found here and there scattered throughout its 

 substance. 



The only treatment that can be recommended is the removal 

 of the tumour at its very earliest stage, and before it has attained 

 any size. If it be of any magnitude no treatment should be 

 attempted, but the animal ought to be fed for slaughter, if not 

 already fit. These tumours do not seem to cause much pain or 

 inconvenience for a long time, and hence the animal will feed 

 well enough. 



X. — CYSTIC TUMOURS. 



These tumours are divided by Paget into simple or barren, 

 and compound or proliferous, the former containing inorganized 

 matter or fluid, the latter various organized bodies. 



The barren cysts contain a fluid-like serum, such as that 

 found in serous abscesses (capped elbow and capped hock), or 

 synovia- like fluid, as in the enlarged bursse (wind-galls) ; 

 whilst others contain a more highly organized fluid, as in 

 ranula. 



These cysts, according to the same authority, have at least 

 three modes of origin. 1st. Some are formed by the enlarge- 

 ment and fusion of the spaces or areolae of the connective or 

 other tissues. In these spaces fluids accumulate ; the tissues 

 become rarefied, and gradually the boundaries of the spaces are 

 levelled down and walled in, till a perfect sac or cyst is formed, 

 the walls of which continue to secrete. 



2d. Some cysts are formed by dilatation and growth of natural 

 ducts or sacculi, as are those sebaceous or epidermal cysts, 

 which, formed by hair follicles, have permanent openings. Such 



