THE GROWTH OF THE BODY.--GROWTH MORE RAPID IN EMBRYONIC PERIOD.--THE
COÖRDINATION AND REGULATION OF GROWTH.--TUMORS.--THE GROWTH OF TUMORS
COMPARED WITH NORMAL GROWTH.--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 coördinated,
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 size at
puberty, and the pituitary body, placed beneath the brain but forming
no part of it, have been shown by recent investigations to have a very
definite relation to growth, especially the growth of the skeleton.
The growth energy chiefly resides in the skeleton, and if the growing
animal has a diet sufficient only to maintain the body weight, the
skeleton will continue to grow at the expense of the other tissues,
literally living upon the rest of the body. Disease of the glands
mentioned leading to an increase or diminution or alteration of their
function may not only inhibit or unduly increase the growth of the
skeleton, but may also interfere with the sexual development which
accompanies the skeleton growth.
The difficulties which arise in an endeavor to comprehend normal
growth are greater when the growth of tumors is considered. A tumor is
a mass of newly formed tissue which in structure, in growth, and the
relations which it forms with adjoining tissues departs to a greater
or less degree from the type of the tissue to which it is related in
structure or from which it originates. It is an independent structure
which, like a parasite, grows at the expense of the body, contributing
nothing to it, and its capacity for growth is unlimited. A tumor
cannot be considered as an organ, its activities not being coordinated
with those of the body. A part of the body it certainly is, but in the
household economy it is to be considered as a wild and lawless guest,
not influenced by or conforming with the regulations of the household.
The rapidity of growth varies; certain tumors for years increase but
little in size, while others may be seen to increase from day to day.
The growth is often intermittent, periods of great activity of growth
alternating with periods of quiescence. The nutrition and growth of a
tumor is only slightly influenced by the condition of nutrition of the
bearer. Its cells have a greater avidity for food than have those of
the body, and, like the growing bones of an insufficiently fed animal,
growth in some cases seems to take place at the expense of the body,
the normal cells not obtaining sufficient nutriment to repair their
waste.
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.
Hæmorrhages 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.
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 coördinated 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.
The traumatic[2] theory. There is much in favor of this. In a certain
number of cases tumors do develop at the site of injuries. The
coincidence of injury and tumor is apt to be overestimated because of
the strong tendency to connect succeeding events. Tumors are not most
common on those parts of the body which are most exposed to injury.
They are rare, for instance, on the hands and feet, and very rarely do
they appear at the site of wounds caused by surgical operations. For
those tumors which develop in intra-uterine life it is difficult to
assign injury as a cause. There does, however, seem to be a relation
between tumors and injuries of a certain character. The natives of
Cashmere use in winter for purposes of heat a small charcoal stove
which they bind on the front of the body; burns often result and
tumors not infrequently develop at the site of such burns. Injuries of
tissue which are produced by the X-ray not infrequently result in
tumor formation and years may elapse between the receipt of the injury
and the development of the tumor. These X-ray injuries are of a
peculiar character, their nature but imperfectly understood, and the
injured tissues seem to have lost the capacity for perfect repair.
In regard to the possible action of both injuries and parasites in
causing tumors, the possibility that their effects on different
individuals may not be the same must be considered. In addition to the
trauma or the parasite which may be considered as extrinsic factors,
there may be conditions of the body, intrinsic factors, which favor
their action in tumor development. The peculiar tissue growth within
the uterus called decidua, which occurs normally in pregnancy and
serves to fasten the developing ovum to the inner lining of the
uterus, may be produced experimentally. This growth depends upon two
factors, an internal secretion derived from the ovary and the
introduction into the uterus of a foreign body of some sort; in the
case of pregnancy the developing embryo acts as the foreign body. It
is not impossible that some variation in the complex relations which
determine normal growth may be one factor, possibly the most
important, in tumor formation.
Another theory is that the tumor is the result of imperfect embryonic
development. The development of the child from the ovum is the result
of a continued formation and differentiation of cells. A cell mass is
first produced, and the cells in this differentiate into three layers
called ectoderm, entoderm and mesoderm, from which the external and
internal surfaces and the enclosed tissues respectively develop, and
the different organs are produced by growth of the cells of certain
areas of these layers. The embryonic theory assumes that in the course
of embryonic development not all the cell material destined for the
formation of individual organs is used up for this purpose, that
certain of the embryonic cells become enclosed in the developing
organs, they retain the embryonic capacity for growth and tumors arise
from them. There is no doubt that something like this does take place.
There is a relation between malformations due to imperfect development
of the embryo and tumors, the two conditions occurring together too
frequently to be regarded as mere coincidence. Also tumors may occur
in parts of the body in which there is no tissue capable of forming
structures which may be present in the tumors. The theory, however, is
not adequate, but it may be among the factors.
The problems concerned in the nature and cause of tumors are the most
important in medicine at the present time. No other form of disease
causes a similar amount of suffering and anxiety, which often extends
over years and makes a terrible drain on the sympathy and resources of
the family. The only efficient treatment for tumors at the present
time is removal by surgical operation, and the success of the
operation is in direct ratio to the age of the tumor, the time which
elapses from its beginning development. It is of the utmost importance
that this should be generally recognized, and the facts relating to
tumors become general knowledge. Tumors form one of the most common
causes of death (after the age of thirty-five one in every ten
individuals dies of tumor); medical and surgical resources are, in
many cases, powerless to afford relief and the tumor stands as a bar
to the attainment of the utopia represented by a happy and comfortable
old age, and a quiet passing. Every possible resource should be placed
at the disposal of the scientific investigation of the subject, for
with knowledge will come power to relieve.
FOOTNOTES:
[1] By cachexia is understood a condition of malnutrition and
emaciation which is usually accompanied by a pale sallow color of the
skin.
[2] By trauma is understood a wound or injury of any sort.