ABNORMAL GROWTH. TUMOURS 261 



inflammation, etc., it is not dangerous to life but remains 

 a local abnormality. It does not give rise to tumours in 

 other parts of the body. Its innocence is frequently 

 emphasised in the formation of a distinct capsule which 

 shuts it off from the surrounding tissue, though at other 

 times such a capsule is absent, and any demarcation between 

 normal and tumour tissue difficult to recognise. Examples 

 of innocent tumours are : Lipoma (composed of fat tissue) ; 

 Fibroma (of fibrous tissue) ; Chondroma (of cartilage) ; 

 Osteoma (of bone) ; Myoma (of muscle tissue) ; Neuroma 

 (of nerve tissue) ; Adenoma (of glandular tissue). 



The Malignant tumour does not remain localised, but 

 infiltrates the surrounding tissues, displacing and destroying 

 their cells ; this is termed " local malignancy." But in 

 addition the growth almost always exhibits " general 

 malignancy " in that it gives rise to other tumours, similarly 

 malignant, in other parts of the body. The two main classes 

 of malignant tumours are the Sarcomas and Carcinomas ; 

 the former originating in connective tissue and to some 

 extent resembling it in structure at times, while the latter 

 develop in one of the many situations where epithelium 

 is present in the body. 



It is to be noted that innocent tumours may, though 

 rarely, develop malignant characters, and also that a tumour 

 with all the microscopic appearances of malignant nature 

 may behave like an innocent one. 



The two chief factors commonly held to predispose to 

 tumour formation are Age, and Injury in some form or 

 another. 



In the evolution of the living growth-cycle two 

 sexual elements unite and lose their identities, and all 

 subsequent cell-multiplication composing the Individual is 

 the wonderful " reaction " which must end inevitably in 

 the multiple restoration of the lost sexual-element 

 identities. 



Where the cells of the Individual are produced in dis- 

 continuity, the theoretically complete Individual ought to 

 be an enormous number of gametes ; but where the Indi- 

 vidual's cells are produced in close continuity this is far 

 from being so. For as part of the Individual develops on 



