PARASITISM. 505 



is effected by the conveyance of juices, in the same way 

 that the. infection of neighbouring parts is, and especially 

 whether the blood takes up anything noxious from the 

 diseased spot and conveys it to a distant place. I must 

 confess that I am acquainted with no sufficiently con- 

 vincing facts bearing upon the matter, and must still 

 allow it to be possible that the diffusion by means of ves- 

 sels may depend upon a dissemination of cells from the 

 tumours themselves. There are, however, many facts, 

 which speak but little in favour of the infections taking 

 place by means of really detached cells, for example, the 

 circumstance that certain processes advance in a direc- 

 tion contrary to that of the current of lymph, so that 

 after a cancer of the breast, disease of the liver takes 

 place whilst the lung remains unaffected. Here it seems 

 pretty probable that juices are taken up, which occasion 

 a further propagation (p. 254). 



Allow me still to add a few words upon a subject which 

 can here be dispatched off hand, namely, the so-called 

 parasitism of new-formations. 



It is self-evident, that the view taken of parasitism by 

 the old writers who held it to be applicable to a large 

 proportion of new-formations, is completely borne out by 

 facts, and that in reality every new-formation which con- 

 tributes to the body no serviceable structures, must be 

 regarded as a parasitical element in the body. Only bear 

 in mind that the idea conveyed by parasitism does not 

 differ from that conveyed by the autonomy of every part 

 of the body excepting in degree, and that every single 

 epithelial and muscular fibre-cell leads a sort of parasiti- 

 cal existence in relation to the rest of the body, just as 

 much as every individual cell in a tree has in relation to 

 the others a special existence, appertaining to itself alone, 

 and deprives the remaining cells of certain matters. Pa- 

 rasitism in a narrower sense of the word, develops itself 



