tissue are called malignant tumors or cancers, but in a strict sense
no tumor can be regarded as benign, for none can serve a useful
purpose. A tumor after a period of slow growth can begin to grow
rapidly. Tumors may arise in any part of the body, but there are
certain places of preference particularly for the more malignant
tumors. These are places where the cells naturally have a marked power
of growth, and especially where growth is intermittent as in the
uterus and mammary gland.

Little is known in regard to the influence of inheritance on the
formation of tumors. Study of the tumors of mice show a slightly
greater susceptibility to tumor formation in the progeny of mice who
have developed tumors. Studies of human families seem to show that
heredity has a slight influence, but in the frequency of tumors such
statistical evidence is of little value. The question of inheritance
has much bearing on the origin of tumors. If the tumor is accidental
and due entirely to extraneous causes, inheritance is not probable;
but if there is some predisposition to tumor formation in certain
individuals due to some peculiarity, then inheritance may exert an
influence.

The question as to whether tumors are an increasing cause of disease
is equally difficult of solution. The mortality statistics, if taken
at their face value, show an enormous increase in frequency; but there
are many factors which must be considered and which render the
decision difficult and doubtful. Tumors are largely a prerogative of
age, and the increased duration of life which preventive medicine has
brought about brings more people into the age when tumors are more
common. Owing to the greater skill in the diagnosis of tumors,
especially those of the internal organs, they are now recognized more