TUMORS. 



343 



have no constant characteristic shape, but vary as much as do the cell 

 forms ill the various glands of the body. Such tumors are conveniently 

 classed together as Carcinoma simplex. 



In addition to these forms there are several others which depend for 

 their characteristics upon various metamorphoses or degenerations, or 

 upon the preponderance of one or other of the anatomical constituents of 

 the growth. It will be most convenient to give a brief description of 

 these various kinds, one after another, with the understanding that they 

 are not absolute specific forms, but are simply varieties which it is con- 

 venient to recognize for clinical as well as anatomical purposes. 



Epithelioma. These tumors occur in the skin and in the mucous mem- 

 branes which are covered with squamous epithelium. The cells present 

 all of the various forms which normally exist in these parts the cuboidal 

 and polyhedral cells of the rete Malpighii, as well as the more superficial 

 flattened forms (Fig. 191). Frequently the spiued cells, or so-called 

 "prickle cells," are largely reproduced. Having to a certain extent the 

 same life history as the cells in which they originate, many of the tumor 



FIG. 191. EPITHELIOMA OF THE NECK. 

 Shows epithelial pearls, spined cells, and reticular masses of variously shaped epithelial cells. 



cells become dry, thin, and horny, like the epidermis. cells, as they grow 

 older ; and since their growth and changes often occur within the old 

 lymph spaces of the affected tissue or in the new-formed alveoli, the 

 cells are sometimes packed together in spheroidal, concentric masses 

 called "epithelial pearls" (Figs. 192 and 193), which may sometimes be 

 seen with the naked eye upon or near the surface of the growth. 



