THE BLASTOMAS 287 



elements composing a tissue. Examples : Congenital 

 angiomata 1 and lymphangiomata, in which from 

 obstruction or other cause the vascular elements of 

 the tissue become unduly prominent, while the normal 

 parenchyma of the part is imperfectly developed. 

 II. Tumours in which one and the same agency leads to abnormal 

 cell relationship and to tumour growth. 



(i.) Tumours in which no primary disturbance of cell re- 

 lationship is to be recognized, the growth originating 

 apparently from functional cells and tissues, and in 

 which so far the causative agent has not been deter- 

 mined. This group would seem to include a very 

 large number of malignant growths epitheliomata 

 of the skin, tongue, etc., carcinomata 2 of the stomach, 

 colon, and so on. The more we study the early 

 stages of cancer the more it is impressed upon us that 

 these would seem frequently (though by no means 

 necessarily always) to develop from the cells of tissues 

 that are or that have been normal and functional, 

 (ii.) Tumours originating from normal and functional tissues 

 through known microbic agency, for example, cocci- 

 diosis of the liver of the rabbit, bilharzia tumours of 

 the bladder and rectum. 



Keviewing the various classes of tumours here rapidly set 

 in order, we recognize a series with at the one extreme tumours 

 originating in misplaced tissue, and growing and continuing to 

 grow without microbic irritation, and at the other extreme 

 tumours originating in normal tissues, and growing as a conse- 

 quence of the low form of irritation induced by parasites. 

 Between these two extremes some approximate and apparently 

 belong to the former group, others show evidences of relationship 

 to the latter. 



Accepting this as the case, it must next be asked, Can we 

 determine anything in common a common denominator, as it 

 were associating these various groups ? Structurally, tumours 

 belonging to the two extremes may be of like nature and histo- 

 logical character, and common denominator there must be, and 



1 [An angioma is a tumour composed of vessels and vascular elements.] 

 1 [A carcinoma is a malignant tumour containing the elements of a glandular 

 epithelium.] 



