CHAPTER XXII. 



TUMOURS. 



CLASSIFICATION. 



Tumours are included in that class of diseases named hyper- 

 trophies or overgrowths ; and all their varieties consist in 

 additions to the organised materials of the body, arising from an 

 excess of formative force ; but in the case of each kind of tumour 

 the mode is peculiar in which this excess is manifested, A 

 tumour differs from an inflammatory exudate in — 1st. That its 

 increase is of itself ; 2d. That it grows as a part of the body by 

 its own inherent force, depending on the surrounding parts for 

 little more than a supply of blood, from which it appropriates 

 its nourishment ; od. As a general rule a tumour increases con- 

 stantly, whereas an inflammatory exudation depends upon a 

 morbid state of the parts at or contiguous to it ; and in- 

 creases in size only so long as the morbid action in the adjacent 

 parts continues. Many tumours are solitary, but it very often 

 happens that many tumours appear almost simultaneously, as 

 in the case of verrucae or warts, in the same animal ; but such 

 multiplicity of primary growths must be distinguished from 

 metastatic formations, or those secondary tumours resulting 

 from the transmission of the elements of an original tumour to 

 other parts of the body characteristic of malignancy. 



Some tumours closely resemble the tissue on and in which 

 they grow, and are consequently called homologous tumours ; 

 whilst others differ very materially from the surrounding tissue, 

 and are called heterologous tumours. For example, a cartilaginous 

 tumour growing from cartilage is homologous, but growing from 

 any other tissue, as from a muscule or a gland, it is heterologous ; 

 thus the same variety of tumour may be in one case homologous 

 and in another heterologous. But heterology is not limited to 



