CHAPTER XXVIII 

 ABNORMAL GROWTH. TUMOURS 



Up to the present time tumour formation has not been 

 satisfactorily explained, in spite of the enormous amount 

 of work which has been done on the subject. It is quite 

 probable, however, that a proper understanding of abnormal 

 growth will not be arrived at until the fundamental processes 

 of normal growth are fully understood. No doubt there 

 are many who believe that at any moment in these days 

 a definite specific agency responsible for the formation of 

 tumours may be discovered, but while this may possibly 

 happen, it does not seem probable. 



The question has really two aspects, one being the nature 

 of tumour formation, and the other the factor or factors 

 inducing it, and the object of the following remarks is to 

 suggest that all neoplasms are exhibitions of one morbid 

 process which can be excited by several different hostile 

 agencies. 



Tumours are divided into two main classes — Simple or 

 Innocent tumours, and Malignant tumours : this is a clinical 

 classification based on the effects produced by them in living 

 organisms. Tumours are also classified as Typical or 

 Atypical, according as their structure conforms to that of 

 normal tissue or not. If the tumour tissue is similar in 

 character to that in which it arises, it is said to be homo- 

 logous ; if of a different type, it is described as heterologous. 

 Thus a lipoma, or fat tumour, growing subcutaneously, is 

 typical, innocent, and homologous, while a cartilaginous 

 tumour arising in bone is innocent, typical, and heterologous. 

 A cancer or sarcoma, on the other hand, no matter where 

 it arises, is malignant, atypical, and heterologous. 



A tumour shows its innocence in that, apart from secon- 

 dary trouble the result of increasing size, pressure effects, 



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