MALIGNANCY 53 



likely that any epithelium in regions where reproductive 

 processes commence may, under some abnormal stimula- 

 tion, develop incompletely determined epithelial products 

 or rudimentary organs. The prodigious fertility of em- 

 bryomas in such products suggests that the imperfect 

 parent tissue is doing its best to be normal, if the phrase is 

 permissible ; but that such a result is impossible, owing to 

 the necessary lack of normal excitation and inhibition, 

 i.e. of the usual environment. That a simple product of 

 epithelium, such as hair, may be perfect is not surprising. 

 The epithelium from which it grows is practically the only 

 environmental stimulus it requires. That teeth, on the 

 other hand, are rudimentary, misshaped, and monstrous, 

 may be regarded as the result of their lacking a normal 

 environment. That embryomas are frequently very 

 deadly is what may be expected from the possibilities of 

 the unspecialized tissues from which they originate. The 

 study of interaction of the various tissues should include 

 far more than the endocrine organs, since it is more 

 than likely to solve the problems of heredity, as well 

 as those of malignant growth. The divisions between 

 physiology, pathology, and biology are responsible in a 

 very large measure for the slowness with which they 

 all advance. 



It follows from all these considerations that it must 

 not be supposed that reaction against one kind of over- 

 growth or the other is due entirely to the tissues principally 

 concerned. Such a view would be a partial denial of the 

 entire independence of the whole organic federation. 

 There is reason to suppose that the blood-stream is hostile 

 to intrusive epithelium. Small cancerous emboli excite 

 thrombosis, and are sometimes buried, and perhaps 

 destroyed, in a blood clot in which lymphocytes are 



