36 WARFARE IN THE HUMAN BODY 



bio tic equilibrium, they certainly do not " explain " 

 malignancy. For it cannot be too frequently insisted on 

 that true explanation is the classification of phenomena 

 under some more inclusive law. Observations, however 

 useful they may prove as regards prevention, are not 

 explanation. For instance, if it be true that atrophy of 

 the thyroid is common, or almost invariable, in cancer, we 

 are not much further advanced in explanation, although in 

 certain cases, say those of familial proneness to malignant 

 disease, such an observation might be useful. 



The sole general results which I am able to extract 

 from the argumentative confusion of the subject is that 

 epithelium and connective tissue somehow or other possess 

 the capacity of invasive aberrancy under long-continued 

 irritation. This may be no more than a re-statement, but 

 it suggests that the only hope of explanation lies in the 

 discovery of the reasons for tissue stability or instability. 

 Is there any reason for supposing that instability or in- 

 vasiveness is in certain conditions a physiological quality in 

 epithelium ? That connective-tissue cells are capable of 

 reparative work of an invasive order we know already. It 

 seems that the reply to the question about epithelium is 

 ready to hand. Bland-Sutton was, perhaps, on the very 

 verge of a possible explanation of cancer when he declared 

 that in the normal action of the trophoblasts of the 

 fertilized ovum could be seen the physiological type of the 

 invasive action of epithelium. In chorion-epithelioma 

 such a physiological type becomes pathological. This 

 dictum implicitly asserts that where the trophoblastic 

 action becomes malignant, there is a loss of balance ; the 

 multi-nuclear cap of the villus is not inhibited by the normal 

 uterine reactions which usually prevent such invasion. 

 What is it in the normal uterus which does inhibit it ? 



