354 THE CAUSATION OF DISEASE. 



cells from a malignant growth, is the peculiar arrangement of 

 the lymphatics in the carcinomata, and the peculiar embryonic 

 condition of the capillaries in the sarcomata. (2) Not only 

 are the tumour cells more frequently carried away from the 

 malignant growths, but the conditions obtaining in the tissues 

 in which they lodge are more favourable for their development 

 than for the development of cells carried away from innocent 

 tumours, because in the former case the transported parasites 

 probably set up an inflammatory hyperemia in the area of 

 secondary infection, and thus the transported tumour cells have 

 a better chance of survival. 



Although, therefore, the presence of the parasite in the site 

 of the secondary tumour probably does actually increase the 

 chance of survival of the transported cell, the parasitic theory is 

 not essential to an explanation of this survival ; but it is needed 

 to explain the fact that the cells thus surviving in the abnormal 

 site take on the same form of retrogressive change as in the 

 primary site. The material conditions being the same in each 

 case, viz. : (1) certain tissue cells ; (2) specific mal-E, the result 

 is in each case the same. 



It would, however, need far more space than I can here give 

 to develop this bacterial theory in all its details, and I must 

 confine myself to its more leading features. There are 

 probably several varieties of " malignant " bacteria. In the 

 first place, the carcinoma parasite must be different from that 

 causing sarcoma ; it differs both as regards its habitat and 

 its virulency. As regards the former, it is apparently in the 

 epithelia alone that it can thrive, but it further differs from 

 the sarcoma parasite in that it is much less virulent. Car- 

 cinomatous tissue is infinitely more complex than sarcomatous, 

 for not only does it contain mature connective-tissue and 

 epithelial cells, but the tissue elements are arranged in a 

 very definite way. Sarcomatous tissue, on the other hand, 

 contains, besides the embryonic blood-vessels, connective-tissue 

 elements only, and these, moreover, in a very immature form, 

 and with little, if any, tendency to definite arrangement. 

 In short, the dissolution is far more complete in sarcoma 

 than in carcinoma, and consequently the irritation must be 

 greater — the parasite must be more virulent. Connective tissue 



