206 MICROBES AND HEALTH. 



Carcinomas are formed in the lymphatic tissue. The 

 spaces between the fibers which form the framework 

 are merely dilated lymph spaces, and these spaces are 

 more or less filled with epithelial cells. The blood- 

 vessels are situated in the connective tissue framework, 

 therefore do not communicate directly with the cells, 

 which lie loose within the spaces, and which constitute 

 the growth. If carcinoma should cause destruction of 

 the connective tissue framework sufficient to reach the 

 blood-vessels, more or less hemorrhage would result and 

 it would then spread by the blood-stream as well as by 

 the lymphatics. As carcinoma or can.oer is always de- 

 rived from epithelial cells, it may occur primarily where- 

 ever these cells are found. These cells cover the muc- 

 ous membrane of the digestive tract, that lining the air- 

 tubes of the lungs; they cover the serous membranes 

 lining all closed cavities, as the abdominal, chest cavity, 

 etc., all glands and their ducts. When cancer is found 

 in other tissues it is secondary, having been carried by 

 the circulation or lymphatics. Those forms of cancer 

 called sarcomas, like carcinomas, are given many 

 names. They are composed of embryonic or newly 

 formed connective tissue cells. Connective tissue forms 

 a framework for all the structures of the body. When 

 resulting from inflammation, the new cells are first 

 small and round, next they elongate into oval or spindle 

 cells, then become hard and fibrous. In sarcoma these 

 cells may undergo no higher change, but remain round, 

 or they may become oval, spindle-shape or fibrous; 

 hence there are round-cell sarcoma, oval-cell sarcoma, 

 and spindle-cell sarcoma. Wl^en there is general fibril- 



