1 8 THE POPULAR SCIENCE MONTHLY 



newly formed cells may form a well-defined mass which simply pushes 

 aside the neighboring parts of the body. After some time the growth 

 may entirely cease or it proceeds usually slowly. In this case we speak 

 of a " benign " tumor. In many other cases, however, the newly formed 

 cells not only multiply, but they also invade the neighboring tissues 

 either as isolated cells or in clusters of cells. Each cell which migrates 

 in the neighboring territory becomes again the center for the forma- 

 tion of a new tumor inasmuch as it has the power for indefinite propa- 

 gation. Other cells even invade the lymph or blood channels of the 

 body, and are carried with the "lymph or blood stream to different parts 

 of the body. At certain places they can not pass the narrow passages, 

 they remain attached to the vessel wall, begin again to multiply, to break 

 through the vessel wall into the neighboring tissue and produce at vari- 

 ous places, often distant from the original site of the tumor, secondary 

 tumors which are called metastases. This infiltrating, metastatizing 

 tumor we call a malignant growth or a cancer. According to the kind 

 of cells which form the cancer and according to the proliferative and 

 infiltrative energy of the cells composing the growth we distinguish 

 many varieties of cancer. There are morphological as well as physio- 

 logical differences between different varieties of cancer. Eoughly we 

 may however classify the various cancers in those derived from epithelial 

 tissue (for instance of the skin, stomach, uterus, the various glands) 

 which we call carcinomata and those derived from proliferating connec- 

 tive tissue cells. Connective tissue in any part of the body may give rise 

 to cancer. These connective tissue cancers are called sarcoma. The 

 growth of a cancer exerts injurious influences on the organism as a 

 whole. Through pressure on neighboring organs it often interferes 

 with important functions of the digestive, respiratory, excretory organs, 

 and leads to serious disturbances of metabolism. It often breaks 

 through the epithelial membranes of the skin or of the inner cavities of 

 the body ; under those conditions parts of the tumor die, break down, and 

 are cast off; an ulcerative surface is thus produced which serves as a 

 place where certain bacteria find a favorable culture medium; putre- 

 faction takes place and the absorption of the putrid material further 

 weakens the organism. But even without the formation of an ulcer, 

 parts of the tumor which are under unfavorable conditions of nourish- 

 ment constantly die (become "necrotic"), while neighboring parts 

 continue to grow. The absorption of the necrotic material may also 

 exert an unfavorable influence on the metabolism. It is furthermore 

 very probable that the living tumor cells give off certain substances 

 which differ quantitatively or qualitatively from the substances pro- 

 duced in the normal organism, but whether these latter substances exert 

 a toxic influence on the organism it is impossible to state at the present 

 time. Cancer almost invariably progresses continuously and it is 



