BARFURTH'S ORDERS OF CELLS 337 



have already given an example of this type of cell in what we 

 said regarding the primitive cells of the myotomes. Such cells 

 Barfurth terms phiripotential. 



With progressive development, once the anlagen of the 

 different tissues have been laid down the cells composing these 

 become more and more differentiated, and now those cells have 

 the capacity to produce one type of tissue only : they become 

 unipotential. 



Consideration will show that tumours group themselves into 

 three great groups exactly corresponding to those three groups 

 of cells laid down by Barfurth. As regards tumours derived 

 from the parasitic growth within the body of one individual, of 

 the products of a separate ovum — twin teratomas — and " filial " 

 teratomas derived from aberrant growth of cells of the germinal 

 type, the products of the reproductive organs of the individual, 

 the cells from which these tumours originate are most simply 

 regarded as being totipotential. It is a far less simple conception 

 to suppose that such tumours are derived from the segregation 

 of a group of cells derived from all three primitive layers. That 

 conception has now been wholly given up. 



Similarly we may regard the whole group of mixed tumours of 

 the Wilms type, the embryomas, as derived from pluripotential 

 cells. If we speak of the first class as teratomas, we may con- 

 veniently refer to these as terato-blastomas, to differentiate them 

 from ordinary tumours formed of one specific type of constituent, 

 with a framework or stroma of indifferent connective tissue and 

 blood-vessels. The latter we must regard as derived from 

 unipotential cells. These we may continue to speak of as the 

 blastomas. 



This method of regarding tumours appears to me both simple 

 and straightforward and helpful in dispersing the doubt and 

 muddle that has existed regarding these transitional types and 

 their relationship. 



We may thus classify new growths as follows : — 



I. Teratomas. — The products of the growth within one in- 

 dividual of what is primarily or potentially another individual. 



(1) Twin or Germinal Teratomas. — Due to the growth within 

 the tissues of the one individual (the host) of the products of 

 another fertilized ovum, coeval with the ovum giving origin 

 to the host. 



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