THE CAUSATION OF DISEASE. 353 



causation. Such an organism accounts for the characteristic 

 feature of the malignant growths — viz., their infectiousness. 



My view is this : Under the bacterial irritation, the tissues 

 are unable to keep at their normal level, and revert to a lower 

 order of tissue, thus exhibiting some one of their many potenti- 

 alities. The type of morbid tissue thus produced depends ( 1 ) 

 upon the nature of the tissue primarily affected and (2) upon 

 the nature of the parasite. 



We have seen that the secondary growths are not always due 

 to the transformation of the affected tissues, and in such cases 

 we cannot say that the affected tissues revert. The secondary 

 tumour in these cases results, I believe, from the transference 

 vf tissue-cells + the bacteria from tlie seat of the primary affec- 

 tion. Under the stimulus of the parasite, these transported 

 cells take on, by virtue of their potentialities, the same 

 morbid action as at the primary seat of infection. It is im- 

 possible, however, to deny the cells of the tissue secondarily 

 affected some share in the process. 



Here, however, a difficulty presents itself. The question 

 may be pertinently asked : Why should the transported cell 

 show such a tendency to grow in the new site ? One can 

 understand, it might be argued, how a specific parasite may 

 cause a reversion in the primary site, but it is not so easy to 

 understand how it can cause the transplanted cell to grow 

 in the secondary site, since this does not occur in the case of 

 innocent tumours. As a matter of fact, however, it has been 

 known to happen. Simple adenoma of the liver has been 

 known to give rise to secondary adenoma of the kidney. This 

 is a very important fact, for it relieves the parasitic theory of 

 what might otherwise be a great difficulty. The greater 

 frequency of secondary growths may, I believe, be explained 

 as follows : — ( 1 ) Certain anatomical peculiarities of the primary 

 tumour permit the transference of the tumour cells. In the 

 innocent tumours the cells are far more fixed than in the 

 malignant, and in reference to this question of fixity it is 

 important to note that the rate of secondary reproduction is 

 generally in direct ratio to the rate at which the primary 

 growth develops ; that is to say, to the looseness of the cells. 

 A further anatomical peculiarity favouring the transference of 



