OWTH.--SIZE, SHAPE AND STRUCTURE OF TUMORS.--
THE GROWTH CAPACITY OF TUMORS AS SHOWN BY THE INOCULATION OF TUMORS OF
MICE.--BENIGN AND MALIGNANT TUMORS.--EFFECT OF INHERITANCE.--ARE
TUMORS BECOMING MORE FREQUENT?--THE EFFECT PRODUCED BY A TUMOR ON THE
INDIVIDUAL WHO BEARS IT.--RELATION OF TUMORS TO AGE AND SEX.--THEORIES
AS TO THE CAUSE OF TUMORS.--THE PARASITIC THEORY.--THE TRAUMATIC
THEORY.--THE EMBRYONIC THEORY.--THE IMPORTANCE OF THE EARLY
RECOGNITION AND REMOVAL OF TUMORS.

The power of growth is possessed by every living thing, but growth is
not limited to the living. Crystals also will grow, and the rapidity
and character of growth and the maximum size of the crystal depends
upon the character of the substance which forms the crystal. From the
single cell or ovum formed by the union of the male and female sexual
cells, growth is continuous until a size corresponding to the type of
the species is attained. From this time onward growth is limited to
the degree necessary to supply the constant loss of material which the
body undergoes. The rapidity of the growth of the body and of its
component parts differs at different ages, and becomes progressively
less active from its beginning in the ovum until the adult type of the
species is attained. As determined by the volume, the embryo increases
more than ten thousand times in size during the first month of
intra-uterine life. At birth the average weight is six and a half
pounds; at the end of the first year eighteen and a half pounds, a
gain of twelve pounds; at the end of the second year twenty-three
pounds, a gain of four and a half pounds. The growth is cooerdinated,
the size of the single organs bearing a definite ratio, which varies
within slight limits, to the size of the body, a large individual
having organs of corresponding size. Knowing that the capacity of
growth is one of the inherent properties of living matter, it is much
easier to understand the continuance of growth than its cessation. It
is impossible to avoid the conclusion that there is some internal
mechanism of the body which controls and regulates growth. In the
first chapter reference was made to organs producing substances which
pass directly into the circulation; these substances act by control of
the activities of other parts, stimulating or depressing or altering
their function. Two of these glands, the thymus, lying in front, where
the neck joins the body and which attains its greatest siz