TUMORS. 



335 



Tumors in Which Epithelial Cells are Predominant or Char- 

 acteristic Elements Epithelial Tumors. 



I. ADENOMA. II. CARCINOMA. 



General Considerations Regarding Epithelial- Cell Tumors. 



While iu the main, in the normal body, the general distinctions 

 between epithelial and other tissues are fairly well marked, there are 

 instances, especially those in which epithelial tissues are in process of 

 physiological growth or rejuvenation, in which the distinctions are quite 

 ill-defined. When we remember the rapid growth of many tumors, the 

 tendency to incomplete formation of their cells, their diverse seats, and 

 the various complicating conditions under which they originate and de- 

 velop, it does not seem strange that the exact limitations of this class of 

 tumors are not easy to fix, nor that they seem sometimes to merge into 

 one another and into tumor tissues belonging to other classes. If epi- 

 thelial cells, under all circumstances, had a definite and characteristic 

 structure, or if, on the other hand, we could always know whether a 



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FIG. 182. CARCINOMA OF THE STOMACH MEDULLARY CARCINOMA OR CARCINOMA MOLLE. 



given cell group originated in epithelium or not, the matter of distin- 

 guishing between tumors of this and other classes would be simple and 

 easy enough. As it is, iu some cases both morphological and histogenetic 

 criteria fail us, and the clinical history and gross appearance are not 

 characteristic. Such instances which are indeed rare suggest the 

 possibility that the facts at our command do not justify such definite 

 distinctions between epithelial and certain other tumors as on both the- 

 oretical and practical grounds we should like to command. While 

 these difficulties in special cases must be acknowledged, the distinctions 

 are in the main definite enough, and very useful both for clinical and 

 scientific purposes. 



