78 TUMORS. 
TUMORS. 
What are tumors ? 
They are new growths in the body composed of the same types of 
tissue as normally exist. They serve no definite purpose in the econ- 
omy of life, and have a certain lawlessness of growth and life history. 
In what shapes do they grow ? 
They may be nodular, tuberous, polypoid, fungoid, papillary, etc. 
How do tumors grow ? 
Either by an increase of internal cell elements (central growth) or 
by growth and increase of cells at their periphery (peripheral growth). 
How are tumors disseminated by metastasis ? 
The tumor cells may get into the blood or lymph vessels and be 
transported to some other part of the body, finally lodging and forming 
an embolus in some vessel. These cells may then proliferate and 
grow, thus forming a so-called metastasis or metastatic tumor. 
How are tumors diagnosed ? 
By the general appearance and arrangement of their structural ele- 
ments, and not by any peculiar or typical cell. 
What are the features of a malignant tumor ? 
Malignant tumors invade adjacent tissues by peripheral growth, and 
are apt to recur after removal. Sooner or later they form metastases, 
and lastly they interfere in a marked way with the nutrition of the 
body and produce a condition known as cachexia. 
In what way do the benign tumors differ from the malignant 
tumors ? 
As a rule, benign tumors grow slower and produce none of the above 
changes. Of course, so-called benign tumors may be serious in effect, 
if, through their position, they interfere with any of the vital functions 
of the body. 
What are the causes of tumors ? 
Mechanical influences, heredity, and possibly bacteria. The theory 
of the embryonal origin of tumors seems at present the most satis- 
factory. This theory is that certain embryonal cells of various kinds 
do not undergo their normal changes, or that they become displaced, 
and thus act as a starting point for the growth of the tumor. Later 
in life these cells may start to grow unrestrained by the influences 
that control normal cells. Just what incites these cells to suddenly 
