506 LECTURE XIX. 



out of this idea of the independence of individual parts. 

 As long as the requirements of the remaining parts de- 

 mand the existence of a part, as long as this part is in 

 any way useful to the other parts, so long will it not be 

 termed a parasite ; but it becomes so from the moment 

 that it becomes foreign or injurious to the body. The 

 epithet, parasitical, must therefore not be restricted to a 

 single class of tumours, but applies to all heteroplastic 

 forms, which do not in the course of their further meta- 

 morphoses give rise to homologous products, but furnish 

 neoplasms which in a greater or less degree are alien to 

 the composition of the body. Everyone of their ele- 

 ments will withdraw matters from the body which might 

 be used for other purposes, and as it has at the very out- 

 set destroyed normal parts and even its first develop- 

 ment presupposes the destruction of its parent structures 

 it both plays a destructive part at the commencement of 

 its career, and a depredatory one throughout its course. 



