358 THE CAUSATION OF DISEASE. 



ported cells in the production of the secondary carcinomata 

 applies also to the secondary sarcomata, but with less force, 

 seeing that connective-tissue elements abound everywhere, and 

 that sarcomatous tissue has no very definite arrangement. 

 We might, with some show of probability, suppose the same 

 sarcoma parasite to bring about the same kind of dissolution, 

 no matter in what tissue it lodged, one kind of bacterium 

 producing round-celled sarcoma, another the giant-celled variety, 

 and so on, in whatever tissue it happened to strand. There 

 is, nevertheless, strong evidence that even in the sarcomata 

 the transported cells share in the production of the secondary 

 growths. I was careful to point out that the giant-celled 

 structure of central bone sarcoma depended rather upon the 

 nature of the tissue primarily affected than upon any special 

 power of the bacterium to cause this particular mode of growth, 

 that in another part this same bacterium would have produced 

 a different kind of sarcoma. Now, inasmuch as secondary 

 myeloid sarcoma of bone exactly resembles the primary growth 

 in structure, the probabilities are very strongly in favour of the 

 former having arisen in large part, not from a transformation 

 of the tissues secondarily affected, but from a multiplication of 

 the transported medullary cells, these behaving under the bac- 

 terial irritation just as in the primary growth. The same line of 

 argument applies to the secondary osteoid sarcomata ; it is 

 not likely that the bony tissue in these growths is due to trans- 

 formation. I have little doubt, however, that this latter pro- 

 cess does take an active share in the secondary sarcomata, more 

 especially as regards round and spindle cells. 



The fact that malignant growths occur by preference in 

 tissues whose vitality is lowered from any cause is strongly 

 in favour of the parasitic theory. There can be little doubt 

 that a continual struggle for existence takes place between the 

 tissue-cells of a multicellular organism on the one hand, and 

 independent unicellular organisms on the other. Under ordinary 

 conditions of health the former obtain the mastery, but what- 

 ever lessens tissue vitality places the tissue-cells at a disad- 

 vantage in the struggle, and hence it is that their diminished 

 vitality favours parasitic development. 



