BENIGN V. MALIGNANT TUMOURS 281 



growth up to a certain point is of the benign type. Hence, 

 if any theory of the parasitic causation of tumours is to conform 

 to the facts already acquired by us as to the life-history of 

 tumours, that theory must assume one of three forms, namely : 



1. That all true tumours, benign as well as malignant, are 

 of parasitic causation. 



2. That infection is but one of a series of causes of tumour 

 growth, both benign and malignant. 



3. That while tumours, as such, need not primarily be of 

 micro-parasitic origin, the assumption of malignant properties 

 is due to infection by parasites, these leading to that active 

 and excessive purposeless cell growth which is the basis of 

 malignancy. 



Let us consider now these possibilities. Are all tumours, 

 benign as well as malignant, of parasitic origin ? 



Definition of the Term " Tumour " 



Before seeking to answer this question, it is necessary to 

 lay down a definition of this term " true tumour." This in 

 itself is no easy matter, for into that definition for our present 

 purposes — and, I may add, equally for general purposes — no 

 definite statement as to causation should be admitted. So 

 long as we are uncertain as to the causation of these growths, 

 our definition must be strictly confined to facts. Ziegler's 

 statement that " a tumour is a new formation of tissue possess- 

 ing atypical structure, not exercising any function of service 

 to the body, and presenting no typical limit of growth," is, on 

 the whole, adequate, though in the existence of such forms as 

 certain adenomata, osteomata, and chondromata the use of the 

 term " atypical structure " requires a little explanation. 



I prefer the definition of C. P. White : " A tumour proper 

 is a mass of cells, tissues or organs resembling those normally 

 present, but arranged atypically. It grows at the expense of 

 the organism, without at the same time subserving any useful 

 function." 1 



1 C. P. White, Journ. of Path, and Bacter. vi., 1899. 



