284 ON GROWTH AND OVERGROWTH 



the growth of these microbes is not sufficient to bring about 

 such an active proliferation and continued vitality on the part 

 of the cells that, carried to other regions, these cells reproduce 

 the primary growth. 



The nematode worm, Bilharzia, an organism vastly higher 

 in the scale of animal life, and one infesting a very large section 

 of the human race, may exist within the organism for long 

 years without setting up any very serious disturbance ; but in 

 those parts of the body which by preference it infests it is clearly 

 capable of producing cell proliferation of an adenomatous, 

 papillomatous, or even of a cancerous type. Living in the radicles 

 of the portal and pelvic vessels, its abundant ova make their 

 way mechanically (on account of their shape) through the vessel 

 walls into the submucosa and mucosa of the lower bowel and 

 the bladder, and so into the lumen of the intestines and the 

 bladder respectively. Numerous cases are on record of extensive 

 neoplasms of the rectum and bladder which are clearly secondary 

 to the continued cell irritation induced by these ova. All, I 

 think, are nowadays prepared, from such cases as these, to 

 agree that there are parasitic agents capable of inducing tumour 

 growth of a benign type ; and, what is more, that this growth 

 does not merely occur in cells which are congenitally displaced, 

 but in those which, prior to irritation, have been portions of 

 strictly normal tissues. 



It would appear, therefore, that the evidence at present in 

 our possession confirms the second possible theory that parasites 

 are but one of the series of causes of tumour growth. 



Now, between these two extremes — forms assuredly due to 

 independent cell growth without microbic intervention, and 

 forms assuredly initiated by microbic intervention — we have a 

 very broad debatable territory, wherein we encounter the main 

 mass of neoplasms. How are we to regard these ? Do they 

 belong to the one or to the other class ? 



Classification of Tumours 



It will be well in the first place to attempt a rapid classi- 

 fication of the different forms, according to the tissues implicated ; 

 according, that is, to the tissues and the cells which give origin 

 to the different forms of tumours. Such a classification is 



