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Page 18
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
frequently and more deaths are correctly ascribed to them. Deaths from
tumors were formerly often purposely concealed and attributed to some
other cause.
No age is immune to tumors. They may be present at birth or develop
shortly afterwards. The age from five to twenty years is the most free
from them, that from forty-five to sixty-five the most susceptible,
particularly to the more malignant forms.
A tumor is a local disease. The growing tissue of the tumor is the
disease, and it is evident that if the entire tumor were removed the
disease would be cured. This is the end sought by surgical
interference, but notwithstanding seemingly thorough removal, the
tumor often reappears after an interval of months or years. There are
many conditions which may render the complete removal of a tumor
difficult or impossible. It is often impossible to ascertain just how
far the tumor cells have invaded the neighboring structures; the
situation of the tumor may be such that an extended removal would
injure organs which are essential for life, or at the time of removal
the tumor cells may have been conveyed elsewhere by the blood or
lymphatic vessels.
Successful removal depends mainly upon the length of time the tumor
has been growing. At an early stage even the most malignant tumor may
be successfully removed. It is evident from this how disastrous may be
the neglect of proper surgical treatment of a tumor. The time may be
very short between the first evidence of the presence of a tumor and
the development of a condition which would render complete removal
impossible.
The effect of a tumor upon its bearer depends upon its character and
situation. Pain is very commonly present, and is due to the pressure
which the growing tumor exerts upon the sensory nerves. Pain may,
however, not be present or appear only at the last. A condition of
malnutrition and emaciation often results due to the passage into the
blood of injurious substances formed in the tumor, or to the
destruction of important organs by the growing tumor. The growth of a
tumor in the intestine may obstruct or close the canal and thus
interfere with nutrition.
The cause or causes of tumors are unknown. We know that the tumor
represents essentially an abnormal growth, and that this growth is due
to new formation of cells. In certain cases the tumor repeats the
structure of the organ or tissue in which it originates, in others it
departs widely from this; always, however, its structure resembles
structures found in the body at some period of life. The tumor cells,
like all other cells of the body, grow by means of the nutriment which
the body supplies; they have no intrinsic sources of energy. The great
problem is what starts the cells to grow and why the growth differs
from that of normal tissue, why it is not regulated and co�rdinated as
are other forms of growth. When a small piece of the skin, for
instance, is cut out growth as rapid as that in tumors takes place in
the adjoining cells, _but it ceases when the loss is restored_.
The same is true when a piece of the liver is removed.
Various hypotheses have been formed to explain the tumor, all of them
of interest, and they have had great importance in that the attempt to
prove or disprove the hypothesis by continued observation and
experiment along definite lines has produced new knowledge. The
various theories as to cause may be divided into three heads.
The parasitic theory. This supposes that a living parasite invades the
body, and by its presence excites the cells of certain tissues to grow
in tumor form. It is known that active growth of the cells of the body
can be excited in a number of ways, by chemical substances such as
certain of the coal tar products, and that it often takes place under
the influence of bacteria. It is further known that parasites can
produce tumor-like growths in plants. The large, rough excrescences on
the oaks are produced by a fly which lays its eggs in or beneath the
bark, and the larva which develops from the egg secretes a substance
which causes the cells about it to multiply, and a huge mass is formed
which serves the developing insect for both food and protection. Large
tumor-like masses are formed on the roots and stalk of cabbages as the
result of the invasion of the cells by a minute organism: the tumors
of olive trees are due to a bacterium; the peculiar growths on cedar
trees, the so-called "witches' brooms," are produced by a fungus, and
there are many other such examples. These have many analogies with
tumors in animals. Under the stimulus of the parasite the cells seem
to have unlimited growth capacity and a greater nutritive avidity than
have the normal plant cells; the character of the mass produced
differs as does the tumor, to a greater or less extent, from the
normal growth; on the cedar, for instance, the "witches' broom"
consists of a thick mass of foliage with small stems less green than
the usual foliage, the leaves wider and not so closely applied to the
stems. The entire plant suffers in its nutrition and a condition
resembling tumor cachexia[1] is produced, and there are no fundamental
differences between the plant and animal tumors. Support has also been
given to the parasitic theory by the discovery within tumor cells of
bodies which were supposed to be a peculiar sort of parasite. If the
truth of the parasitic theory could be proved, there would be
justifiable expectation that the tumor disease might be controlled as
are many of the parasitic diseases, but the hypothesis awaits the
demonstration of its correctness. Despite the study of tumors which is
being actively pursued in many places and by the most skilled
investigators, no parasites have been found in animal tumors; the
objects previously described as parasites have been found not to be
such. It is difficult to bring in accord with the parasitic theory the
great variation in tumor structure, the relation of certain tumors, as
the malignant tumors of the breast and uterus, with the age of the
bearer, the congenital tumors which develop in intra-uterine life, and
there are many other conditions which oppose the theory.
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