EPITHELIAL TUMORS. 83 
What is a papilloma ? 
It is a tumor formed of enlarged papilli covered by epithelium. It 
may be situated either on a skin or mucous membrane surface. 
Describe an adenoma. 
It is a tumor formed by a reproduction of typical gland tissue. The 
structure of the cellular elements and their arrangement into alveoli 
and ducts vary widely. The irregularities of their growth often lead 
to a stoppage of the ducts and alveoli and formation of cysts. 
Of what is a carcinoma composed ? 
Jt is a malignant tumor composed of a connective-tissue stroma 
forming more or less well-defined communicating spaces or alveoli, in 
which lie various-shaped epithelial cells. The cells in these alveolar 
spaces are not attached to their walls, and there is no fibrillated inter- 
cellular substance between the cells as in sarcoma tissue. 
Into what varieties may the various forms of carcinomata be 
classified ? 
Gland-celled carcinoma, cylindrical-celled carcinoma, flat-celled 
carcinoma or epithelioma, colloid carcinoma, melano-carcinoma and 
carcinoma myxomatoides. 
Describe a gland-celled carcinoma. 
It is characterized by its alveolar structure and by the absence of 
any special characteristic shape to its cells, which may be fusiform, 
polyhedral, cuboidal or spheroidal. The tumor may be hard or soft 
according to the relative amount of fibrous stroma present. If the 
fibrous tissue is abundant the tumor is hard and firm (sctrrhus carci- 
noma). If scanty in amount the tumor is soft (medullary cancer or 
carcinoma molle). 
What is a cylindrical-celled carcinoma ? 
It is made up like the preceding form, with the exception that a 
greater or less number of the cancer cells are cylindrical in shape. 
What are the peculiarities of epitheliomata ? 
They usually occur on the skin or mucous membranes. The cells 
resemble those normally existing in these tissues, and have a similar 
life history. In some of the tumors of this variety the flattened cells 
are often packed about a central point concentrically. These are called 
bird-nest bodies or epithelial pearls, 
What is a colloid carcinoma ? 
It is a carcinoma, the cells of which have become infiltrated with 
