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Page 17
A tumor may be of any size: so small as to be invisible to the naked
eye, or its weight may exceed that of the individual who bears it. The
limitations to its growth are extrinsic and not intrinsic. There is no
distinct color. Certain tumors have color which depends upon the
presence of a dark brown or black pigment within the cells.
H�morrhages within them are not infrequent, and they may be colored by
the blood or by pigments formed from it. Usually they have a gray
color modified by their varying vascularity, or the cut surface may be
mottled due to areas of cell degeneration. The consistency varies;
some tumors are so soft that they can be pressed through a sieve,
others are of stony hardness. There is no distinct shape, this being
influenced by the nature of the tumor, the manner of growth and
situation. When the tumor grows on or near a surface, it may project
from this and be attached by a narrow band only; in the interior of
the body it may be irregular in outline, round or lobular, the shape
being influenced by many factors. Tumors like the tissues of the
normal body are nourished by the blood and contain blood vessels often
in great numbers.
A tumor arises by the cells of a part of the body beginning to grow
and taking on the characteristics of a tumor. Its growth is
independent, the cells of the adjoining tissue taking no part in it.
The tissue in the vicinity of the tumor is partly pushed aside by the
mass, or the tumor grows into it and the tissue disappears as the
tumor advances. The destruction of the surrounding tissue is brought
about partly by the pressure which the tumor exerts, partly by the
compression of the blood vessels or the blood supply of the organs is
diverted to the tumor.
The characteristics of a tumor are due to the cells which it contains
(Fig 14). These often become separated from the main mass and are
carried by the blood into other parts of the body, where they grow and
form tumors similar in character to the parent tumor. In the
extraordinary capacity for growth possessed by tumor cells, they
resemble vegetable rather than animal cells. There is no limit to the
growth of a tumor save by the death of the individual who bears it,
thus cutting off the supply of nutrition. The cells of tumors peculiar
to man show a narrow range of adaptation. They will grow only in the
body of the individual to whom the tumor belongs, and die when grafted
on another individual. In the case of tumors which arise in animals,
pieces of the tumor when grafted on another animal of the same species
will grow, and in this way the growth capacity of the tumor cells has
been estimated. Thus, by transplanting a small section of a mouse
tumor into other mice, the small transplanted fragments will in two
weeks grow to the size of filberts, and each of these will furnish
material to engraft upon ten mice. These new tumors are similar in
character to the original tumor, and really represent parts of it in
the same way that all the Baldwin apples in the world are parts of the
original tree which was found in Baldwinville many years ago, and as
all the Concord grape vines are really parts of the original vine. It
has been estimated that if all the growth capacity of this mouse tumor
were availed of by the successive inoculation of other mice, a mass of
tumor several times the diameter of the sun would grow in two years.
The condition of the individual seems to exert no influence upon the
growth of the tumor. Growth may be as rapid when the bearer is in a
condition of extreme emaciation as it is when the bearer is well
nourished and robust.
[Illustration: FIG 14.--PHOTOGRAPH OF A MICROSCOPIC PREPARATION FROM A
CANCER OF THE UTERUS. A large mass of cells is extending into the
tissue of the uterus which is shown as the fibrous structure. Such a
cell mass penetrating into the tissue represents the real cancer, the
tissue about the cell masses bear the blood vessels which nourish the
tumor cells.]
Those tumors which grow rapidly and invade and destroy the surrounding
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.
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