TUMOES. 



Classification of Tumors. 



It is. not possible to-day to make a satisfactory scientific classification 

 of tumors ; but the fact that they are composed of structures which re- 

 semble the various morphological types of tissue found in the normal 

 body suggests a grouping of the various forms which may be regarded 

 as a useful and suggestive catalogue. 



It should be remembered that the usual separation of the normal tis- 

 sues into groups is useful, rather because it facilitates their study than 

 because it expresses absolute and fundamental distinctions ; and the same 

 may be said of all the classifications of tumors. An increase of our 

 knowledge concerning their structure and genesis will doubtless lead to 

 a more accurate grouping of tumors ; but for the present such an arrange- 

 ment as that indicated below will be found of practical value for the pur- 

 poses of study. ' 



CONNECTIVE-TISSUE TYPE. 

 Normal Tissue. Tumors. 



Fibrillav connective tissue. Fibroma. ^ ^ 



Mucous tissue. Myxoma. ^ * 



Embryonal connective tissue. Sarcoma. *^ - 



Endothelial cells. Endothelioma. " 



Fat tissue. Lipoma.K^" 



Cartilage. Chondroma. *- 



Bone. Osteoma. """' 



Neuroglia. 2 Glioma. ^ 



MUSCLE-TISSUE TYPE-MYOMATA. 



Normal Tissue. Tumors. 



Smooth muscle tissue. Leiomyoma. ^ 



Striated muscle tissue. Rhabdomyoma. ^ 



1 The attempt has often been made to classify tumors with reference to the develop- 

 mental history of the tissues represented, and it has been generally believed that cells 

 once differentiated in the primary embryonic layers cannot again be merged in type. 

 While this principle holds good in general, especially for highly differentiated forms, 

 certain recent studies have seemed to indicate that even this distinction may not be 

 inflexible. However this may be, it is certain that the cells derived from one embry- 

 onic layer may under special conditions come so closely to resemble in morphology those 

 of another layer, that a structural differentiation, with our present resources at least, 

 is not always possible. While, therefore, this, which is called the histogenetic principle 

 of dassifiation, is most suggestive and may be useful in connection with other data in 

 the study of tumors, it seems to the writer that it is wiser for the present not to base our 

 classification loo largely upon embryological data in several particulars still subject to 

 controversy. 



Consult in this connection the resume of Marcliand on "The Relationship between 

 Pathological Anatomy and Embryology," Verh. d. deutschen path. Gesellschaft, Bd. ii., 



See also the admirable address by Minot on " The Embryological Basis of Pathology, " 

 Science, March 29th, 1901. In this paper, p. 487, the tissues are classified in accordance 

 with their genetic relationships. 



2 The neuroglia, as well as the tumors derived from it, presents marked peculiari- 

 ties in structure. While the neuroglia is closely related in genesis to the nervous sys- 

 tem, being of ectodermal origin, its structural and functional alliance with the connec- 

 tive tissues of the mesoderm seems to the writers to justify for the present purpose its 

 grouping among the latter. 



