TUMORS. 



293 



ments of the cells. Those new cells formed in tumors which are char- 

 acteristic of the growth are all descendants of the cells in which the 

 neoplasm starts and maintain their general type. But the old tissue of 

 the part in which the tumor grows may remain with its vessels and form 

 a matrix whose interstices are filled with the new tumor tissue; or the old 

 tissue may furnish the starting-point for a new growth of a fibrous and 

 vascular nutrient and sustaining 

 stroma. 



Metastasis of Tumors. All tu- 

 mors are not limited, as we have 

 seen, to that part or region of the 

 body in which they first occur. 

 Sooner or later secondary nodules 

 resembling the first may be found 

 in distant parts of the body, some- 

 times singly, sometimes in great 

 numbers. These may grow like 

 the parent tumor, and them- 

 selves form foci for new dis- 

 seminations. 



This dissemination of tumors 

 is one of the most important 

 elements of malignancy, and is 

 called metastasis, the secondary 

 tumors being called metastatic 

 tumors. This occurs by the trans- 

 portation of tumor cells through 

 the blood or lymph channels 

 (Fig. 142). Since the tumor it- 

 self may contain new and badly 

 formed blood and lymph vessels, 

 and its structures be in close con- 

 tact with the vessels of the tissue 

 in which it grows, the cells of 

 the primary tumor may, by ul- 

 ceration through or by atrophy 

 of the walls, readily find their 

 way into the lumen of the vessels and be swept away by currents as 

 emboli, and, finding lodgment, proliferate and grow, forming secondary 

 tumors; or the proliferation may occur in the vascular endothelium 

 itself, when the formation of emboli is easy to understand. When carried 

 through the lymph vessels the tumor cells may for some time be kept 

 from the larger channels and from general dissemination by lodgment 

 in the lymph-nodes, where they may establish independent tumors. 



The tumors in which metastasis is most apt to occur are, as a rule, 

 those which grow rapidly, are vascular and succulent, and contain many 

 cells. The Darts of the body in which metastatic tumors are most apt to 



FIG. 141. A nodular polypoid tumor fibroma hanging 

 , from the vulva. 



