292 



TUMORS. 



new tumors. Many tumors are sharply circumscribed, may be even en- 

 capsulated, and influence surrounding parts only by the pressure which 

 they exert upon them. In this way they may cause displacement, atro- 

 phy, or necrosis ; they may, by pressure on neighboring vessels, induce 



oedema, thrombosis, etc. ; 

 they may in the same way 

 lead to dislocation and ca- 

 ries of bones. 



Tumors may grow largely 

 by increase of elements with- 

 in them, thus simply expand- 

 ing; this is called central 

 growth. They may grow in 

 part or largely at the sur- 

 face peripheral growth. In 

 this case the growth may be 

 a direct, continuous enlarge- 



FIG. 139. MULTIPLE NODULAR SARCOMATA OF THE SKIN. llieilt of the mass at or near 



the periphery, or it may be 



by the formation of secondary nodules near the primary growth, which, 

 gradually enlarging, finaly coalesce with the latter, forming a part of 

 the nodular tumor. This mode of enlargement is called discontinuous 



FIG. 140. SARCOMA OF THE FOREAUM. A tumor of the tabulated type. 



peripheral groicth, and is due to the dissemination of cells from the mother 

 tumor into the adjacent tissue through the blood or lymph channels, and 

 their proliferation at the points of lodgment. This dissemination may 

 occur by the agency of blood or lymph currents or by the amoeboid move- 



