400 



Tumors. 



The dissemination of the cancer into the tissues, as above indi- 

 cated, occurs primarily from the penetration of the multiplying epi- 

 thelium into the lymph spaces. They here form tubular or solid 

 laminated cords, push aside the endothelium and other connective 

 tissue elements, and by continuous progression of growth force their 

 way deeper into the tissues, between the muscle fibres and beyond. 

 In this way, for example, a growth on the surface of a mucous 



Fig. 118. 

 Lung of dog with metastatic cancer nodes (tliyroid cancer). 



membrane forces its way through the muscularis mucosa and onward 

 into the muscular tunics and serous coat of the tube. In the lymph 

 passages, by continuity of growth the cords of cancer cells may 

 extend as far as the nearest lymph glands ; or individual cells loos- 

 ened in some way may be carried by the lymph current to the latter 

 and to more distant portions of the lymphatic system. Multiplica- 

 tion of the tumor cells in the tissue of the lymph nodes, and the re- 

 active inflammatory proliferation of the connective tissue of these 



