TUMORS. 355 



Mucous tissue is best studied in the fresh condition by pressing 

 small bits flat between a cover-glass and slide. The processes of 

 the cells may then be seen in their continuity ; while, if sections 

 are prepared after hardening, many of those processes will be cut 

 in such a way that their connections with the cells in the contiguous 

 sections are destroyed, and they appear as fibres lying free in the 

 intercellular substance. 



Mucous tissue must be carefully distinguished from cedematous 

 fibrous tissue. Such oedematous tissue possesses cells of a spindle 

 or flat shape, like those usually met with in fibrous tissue ; but 

 the usual fibrous intercellular substance has a loosened texture, 

 due to the presence of fluid between the fibres, which gives the 

 tissue a soft, transparent character not unlike that of mucous tissue. 

 It must also be borne in mind that fibrous and adipose tissues are 

 liable to undergo a mucous degeneration in which the cells assume 

 a more stellate form than is usual with those tissues, and the inter- 

 cellular substances lose their fibrous character and become more 

 homogeneous. Such degenerations are distinguished with difficulty 

 from the tissue which originally develops as mucous tissue, but 

 they have nothing in common with tumors. 



Myxomata usually develop in fibrous tissue, adipose tissue, or the 

 medulla of bone. In association with cartilage they are not un- 

 common in the parotid gland. When pure they are benign, but 

 their association with sarcoma often gives them a malignant char- 

 acter, the degree of malignancy depending upon that of the sar- 

 comatous tissue present. 



6. Endothelioma. Theendotheliomata are connective-tissue tumors 

 which owe their origin to a proliferation of the flat endothelial cells 

 that line the serous cavities, line or form the walls of the blood- 

 vessels and lymphatics, and are present in some of the lymph and 

 other spaces of the fibrous tissues. Young cells of this variety do 

 not have the membranous bodies that characterize the fully devel- 

 oped older cells, but closely resemble the cells of epithelium. It 

 follows that in this class of tumors it is not always easy to 

 determine the origin of the cells from a mere inspection of 

 their shapes and sizes. The situation and general structure of 

 the tumor will often decide this point. Epithelial tumors spring 

 from pre-existent epithelium, either in some normal site or in an 

 unusual situation because of some anomaly of development (e. <?., 

 in the neck, owing to imperfect obliteration of the branchial clefts). 



