394 Tumors. 



mentioned as destructive or malignant adenoma or adenocarcinoma 

 is essentially cancerous in its nature and is malignant both bv local 

 extension and by metastasis. Any adenoma may be regarded with 

 suspicion and dealt with accordingly, when it is recalled that it is not 

 very uncommon for these growths to lose their purely adenomatous 

 character and become changed into adenocarcinomata.] 



Carcinomata. 



A carcinoma or cancer is a malignant new growth composed of 

 epithelium and connective tissue, characterized by a persistent and 

 progressive penetration of its epithelial elements into the underl> ing 

 tissues. The cancers always originate from epithelium, either surface 

 epithelium or the glandular epithelial cells of functionating organs, 

 or from islets of epithelial cells formed in foetal life and occurring 

 in unusual situations. They may also take tlieir origin from pre- 

 viously existing papillomata, adenomata and cystomata, these having 

 from unknown cause assumed a proliferation of their epithelial cells 

 with departure from their ordinary forms and boundaries. 



The proliferating epithelium forming the cancerous parenchvma 

 or body of the cancer behaves as a foreign intruder ; It assumes 

 an independent status by no longer remaining confined to the surface 

 which it previously covered, breaking through its normal limiting 

 structures and playing the part of epithelial cells which have be- 

 come practically parasitic. These cells, derivatives of previously 

 existing epithelium, by their penetrative growth and active multi- 

 plication usually form in the deeper structures solid cords or duct- 

 like processes which branch like the roots of a tree and are contin- 

 ually sending out new projections into the tissue. These retain- 

 ing their continuity with each other result in forming a network 

 or meshwork [of epithelial character throughout the invaded 

 tissue] varying in its density and with irregular nodal point? 

 (Ribbert). This net-like and corded arrangement of the epithelial 

 roots is due to the fact that the cells in their penetration follow the 

 lines of least resistance and therefore penetrate the lumen of the 

 lymph passages, come to completely fill them with their growth and 

 therefore to assume their shape. After occupying all the lymph 

 spaces of the connective tissue the epithelial roots may penetrate 

 into the tissue itself in such numbers as to practically constitute a 

 difl-'use infiltration (Ribbert). 



In microscopic sections the continuity of the cords is not entirely appre- 

 ciated, as each sectional layer, of course, contains only segments of them. 



