326 Tumors. 



sometimes rapidly, and never undergoing diminution, they inter- 

 fere with the other tissues, perhaps by robbing them of their 

 nutrition, perhaps by some of the products of their metaboHc 

 changes, but particularly in a mechanical way by their pressure 

 influences. 



It has been only within the last sixty years, since Rudolf 

 Virchow by comprehensive histological studies and critical 

 examination of the older literature established a new basis for 

 the systematic consideration of the different types of tumors, 

 that a scientific conception of the origin and nature of new 

 growths has entered into their study {oncology; 6 6yKos, node). 

 Previous to this period tumors were classified mainly from their 

 external appearances and their gross anatomical characteristics, 

 and were named frequently from incidental features often of 

 merely accidental prominence ; and no real knowdedge was had 

 of the developmental history of these growths. Although in 

 our present knowledge of the development of tumors there are 

 many missing links, we nevertheless possess from microscopic 

 and experimental investigations sufficient information in regard 

 to their nature to permit us to clearly recognize* their derivation 

 from the cells of the body, the mode of their extension and their 

 actual method of growth, and the significance of the pathological 

 process in its bearing upon the life of the subject. 



Tumors may te classified from their histogenesis, that is, 

 from their structure and from their origin and construction from 

 the cells and tissues of the body. There are no foreign tumor ele- 

 ments brought into the body from without ; tumors are offsprings 

 of the body cells, and are accordingly found to consist of these 

 and of the intercellular substances of the various tis-;ues. They 

 develop according to the same laws which govern the embryonic 

 development and later growth of the individual and the processes 

 of regeneration ; and they arise from the four primary types of 

 body tissue (connective tissue in all its forms, epithelium, muscle 

 and nervous tissue.) 



Just as the tumor cells present the same form and the same 

 mode of multiplication as the mother cells from which they are 

 derived, the intercellular substances, as products of the cells, are 

 the same as are produced by the original cells. Generally, there- 

 fore, the source of a tumor can be determined from the character 

 of its tissue ; although because of the fact that they grow^ more 

 or less independently, as isolated masses of tissue, it is quite 

 reasonable to expect more or less modifications in the structure 



