Repair, other things being equal, takes place more easily in the young than in the old. New formation of cells goes on with great rapidity in intra-uterine life, the child, beginning its existence as a single cell one two hundred and fiftieth of an inch in diameter, attains in nine months a weight of seven pounds. The only similar rapidity of cell formation is seen in certain tumors; although the body may add a greater amount of weight and in a shorter time, by deposit of fat, this in but slight measure represents a new formation of tissue, but is merely a storage of food material in cells. The remarkable repair and even the new formation of entire parts of the body in the tadpole will not take place in the completely developed frog.

Repair will also take place the more readily the less complicated is the architectural structure of the part affected. When a series of tissues variously and closely related to one another enter into the structure of an organ, there may be new formation of cells; but when the loss involves more than this, the complicated architectural structure will not be completely replaced. A brick which has been knocked out of a building can be easily replaced, but the renewal of an area of the wall is more difficult. In the kidney, for example, the destruction of single cells is quickly made good by new cell formation, but the loss of an area of tissue is never restored. In the liver, on the other hand, which is of much simpler construction, large areas of tissue can be newly formed. For the formation of new cells in a part there must be a sufficient amount of formative material; then the circulation of the blood becomes more active, more blood being brought to the part by dilatation of the vessels supplying it.

Repair after a loss can be perfect or imperfect. The tissue lost can be restored so perfectly that no trace of an injury remains; but when the loss has been extensive, and in a tissue of complex structure, complete restoration does not take place and a less perfect tissue is formed which is called a scar. Examination of the skin in almost anyone will show some such scars which have resulted from wounds. They are also found in the internal organs of the body as the result of injuries which have healed. The scar represents a very imperfect repair. In the skin, for example, the scar tissue never contains such complicated apparatus as hair and sweat glands; the white area is composed of an imperfectly vascularized fibrous tissue which is covered with a modified epidermis. The scar is less resistant than the normal tissue, injury takes place more easily in it and heals with more difficulty.

Loss brought about by the injuries of disease can be compensated for, even when the healing is imperfect, by increased function of similar tissue in the body. There always seems to be in the body under the usual conditions a reserve force, no tissue being worked to its full capacity. Meltzer has compared the reserve force of the body to the factor of safety in mechanical construction. A bridge is constructed to sustain the weight of the usual traffic, but is in addition given strength to meet unusual and unforeseen demands. The stomach provides secretion to meet the usual demands of digestion, but can take care of an unusual amount of food. The work of the heart may be doubled by severe exertions, and it meets this demand by increased force and rapidity of contraction; and the same is true of the muscles attached to the skeleton. The constant exercise of this reserve force breaks down the adjustment. If the weight of the traffic over the bridge be constantly all that it can carry, there quickly comes a time when some slight and unforeseen increase of weight brings disaster. The conditions in the body are rather better than in the case of the bridge, because with the increased demand for activity the heart, for example, becomes larger and stronger, and reserve force rises with the load to be carried, but the ratio of reserve force is diminished.

This discussion of injury and repair leads to the question of old age.

Old age, as such, should not be discussed in a book on disease, for it is not a disease; it is just as natural to grow old and to die as it is to be born. Disease, however, differs in many respects in the old as compared with the young and renders some discussion of the condition necessary. Changes are constantly taking place in the body with the advance of years, and in the embryo with the advance of days.

In every period of life in the child, in the adult, in the middle-aged and in the old we meet with conditions which were not present at earlier periods. There is no definite period at which the changes which we are accustomed to regard as those of old age begin. This is true of both the external appearances of age and the internal changes.

One individual may be fully as old, as far as is indicated by the changes of age, at fifty as another at eighty.

With advancing age certain organs of the body atrophy; they become diminished in size, and the microscopic examination shows absence or diminished numbers of the cells which are peculiar to them. The most striking example of this is seen in the s.e.xual glands of females, and, to a less degree, in those of the male. There is a small ma.s.s or glandular tissue at the root of the neck, the thymus, which gradually grows from birth and reaches its greatest size at the age of fifteen, when it begins slowly to atrophy and almost disappears at the age of forty. This is the gland which in the calf is known as the sweetbread and is a delicious and valued article of food. The tonsils, which in the child may be so large as to interfere with breathing and swallowing, have almost disappeared in the adult; and there are other such examples.

In age atrophy is a prominent change. It is seen in the loss of the teeth, in the whitening and loss of the hair, in the thinning of the skin so that it more easily wrinkles, in the thinning and weakening of the muscles so that there is not only diminished force of muscular contraction, but weakening of the muscles of support. The back curves from the action of gravity, the strength of the support of the muscles at the back not counteracting the pull of the weight of the abdominal viscera in front. The bones become more porous and more brittle.

The effect of atrophy is also seen in the diminution of all functions, and in loss of weight in individual organs. That the brain shares in the general atrophy is evident both anatomically and in function.

Mental activity is more sluggish, impressions are received with more difficulty, their accuracy may be impaired by accompanying changes in the sense organs, and the concepts formed from the impressions may differ from the usual. The slowness of mental action and the diminution in the range of mental activity excited by impressions, and the slowness of expression, may give a false idea of the value of the judgment expressed. The expression changes, the face becomes more impa.s.sive because the facial muscles no longer reflect the constant and ever changing impressions which the youthful sense organs convey to a youthful and active brain. That the young should ape the old, should seek to acquire the gravity of demeanor, to restrain the quick impulse, is not of advantage. Loss of weight of the body as a whole is not so apparent, there being a tendency to fat formation owing to the non-use of fat or fat-forming material which is taken into the body.

One of the most evident alterations is a general diminution in the fluid of the tissues, to which is chiefly due the lack of plumpness, the wrinkles of age. The facial appearance of age is given to an infant when, in consequence of a long-continued diarrhoea, the tissues become drained of fluid. Every market-man knows that an old animal is not so available for food, the tissues are tougher, more fibrous, not so easily disintegrated by chewing. This is due to a relative increase in the connective tissue which binds all parts together and is represented in the white fibres of meat.

Senile atrophy is complex in its causes and modes of production. The atrophy affects different organs in different degree and shows great variation in situation, in degree and in progress. Atrophic changes of the blood vessels are of great importance, for this affects the circulation on which the nutrition of all tissues depends. While there is undoubted progressive wear of all tissues, this becomes most evident in the case of the blood vessels of the body. It is rare that arteries which can be regarded as in all respects normal are found in individuals over forty, and these changes progress rapidly with advancing age. So striking and constant are these vascular changes that they seem almost in themselves sufficient to explain the senile changes, and this has been frequently expressed in the remark that age is determined not by years, but by the condition of the arteries.

Comparative studies show the falsity of this view, for animals which are but little or not at all subject to arterial disease show senile changes of much the same character as those found in man.

There is another condition which must be considered in a study of causes of age. In the ordinary course of life slight injuries are constantly being received and more or less perfectly repaired. An infection which may but slightly affect the ordinary well-being of the individual may produce a considerable damage. Excess or deficiency or improper food, occasional or continued use of alcohol and other poisons may lead to very definite lesions. Repair after injury is rarely perfect, the repaired tissue is more susceptible to injury, and with advancing age there is constant diminution in the ease and perfection of repair. The effect of the sum of all these changes becomes operative: a vicious circle is established in which injury becomes progressively easier to acquire and repair constantly less perfect. There is some adjustment, however, in that the range of activities is diminished, the environment becomes narrower and the organism adapts its life to that environment which makes the least demands upon it.

Whether there is, entirely apart from all conditions affecting nutrition and the effect of injuries which disturb the usual cell activities, an actual senescence of the cells of the body is uncertain. In the presence of the many factors which influence the obvious diminution of cell activity in the old, it is impossible to say whether the loss of cell activity is intrinsic or extrinsic. The life of the plant cell seems to be immortal; it does not grow old.

Trees die owing to accidents or because the tree acquires in the course of its growth a ma.s.s of tissue in which there is little or no life, and which becomes the prey of parasites. The growing tissue of a tree is comprised in a thin layer below the bark, and the life of this may seemingly be indefinitely prolonged by placing it in a situation in which it escapes the action of accidental injuries and decay, as by grafting on young trees. Where the nature of the dead wood is such that it is immune from parasites and decay, as in the case of the Sequoias, life seems to be indefinitely prolonged. The growing branches of one of these trees, whose age has been estimated with seeming accuracy at six thousand years, are just as fresh and the tree produces its flowers and fruit in the same degree as a youthful brother of one thousand years. Nor does old age supervene in the unicellular organisms. An amoeba a.s.similates, grows and multiplies just as long as the environment is favorable.

Old age in itself is seldom a cause of death. In rare cases in the very old a condition is found in which no change is present to which death can be attributed, all organs seem to share alike in the senescence. Death is usually due to some of the accidents of life, a slight infection to which the less resistant body succ.u.mbs, or to the rupture of a weakened blood vessel in the brain, or to more advanced decay in some organ whose function is indispensable. The causes and conditions of age have been a fertile source for speculation. Many of the hypotheses have been interesting, that of Metschnikoff, for example, who finds as a dominating influence in causing senescence the absorption of toxic substances formed in the large intestine by certain bacteria. He further finds that the cells of the body which have phagocytic powers turn their activity against cells and tissues which have become weakened. There may be absorption of injurious substances from the intestines which the body in a vigorous condition is able to destroy or to counteract their influence, and these may be more operative in the weaker condition of the body in the old.

Phagocytes will remove cells which are dead and often cells which are superfluous in a part, but there is no evidence that this is ever other than a conservative process. Since it is impossible to single out any one condition to which old age is due, the hypothesis of Metschnikoff should have no more regard given it than the many other hypotheses which have been presented.

Death of the body as a whole takes place from the cessation of the action of the central nervous system or of the respiratory system or of the circulation. There are other organs of the body, such as the intestine, kidney, liver, whose function is essential for life, but death does not take place immediately on the cessation of their function. The functions of the heart, the brain and the lungs are intimately a.s.sociated. Oxygen is indispensable for the life of the tissues, and its supply is dependent upon the integrity of the three organs mentioned, which have been called the tripos of life.

Respiration is brought about by the stimulation of certain nerve cells in the brain, the most effective stimulus to these cells being a diminution of oxygen in the blood supplying them. These cells send out impulses to the muscles concerned in inspiration, the chest expands, and air is taken into the lungs. Respiration is then a more complicated process than is the action of the heart, for its contraction, which causes the blood to circulate, is not immediately dependent upon extrinsic influences. Death is usually more immediately due to failure of respiration than to failure of circulation, for the heart often continues beating for a time after respiration has ceased.

Thus, in cases of drowning and suffocation, by means of artificial respiration in which air is pa.s.sively taken into and expelled from the lungs, giving oxygen to the blood, the heart may continue to beat and the circulation continue for hours after all evident signs of life and all sensation has ceased.

By this general death is meant the death of the organism as a whole, but all parts of the body do not die at the same time. The muscles and nerves may react, the heart may be kept beating, and organs of the body when removed and supplied with blood will continue to function.

Certain tissues die early, and the first to succ.u.mb to the lack of oxygenated blood are the nerve cells of the brain. If respiration and circulation have ceased for as short a time as twelve minutes, life ceases in certain of these cells and cannot be restored. This is again an example of the greater vulnerability of the more highly differentiated structure in which all other forms of cell activity are subordinated to function. There are, however, pretty well authenticated cases of resuscitation after immersion in water for a longer period than twelve minutes, but these cases have not been carefully timed, and time under such conditions may seem longer than it actually is; and there is, moreover, the possibility of a slight gaseous interchange between the blood and the water in the lungs, as in the case of the fish which uses the water for an oxygen supply as the mammal does the air. There are also examples of apparent death or trances which have lasted longer, and the cases of fakirs who have been buried for prolonged periods and again restored to life. In these conditions, however, all the activities of the body are reduced to the utmost, and respiration and circulation, so feeble as to be imperceptible to ordinary observation, suffice to keep the cells living.

With the cessation of life the body is subject to the unmodified action of its physical environment. There is no further production of heat and the body takes the temperature of the surroundings. The only exceptions are rare cases in which such active chemical changes take place in the dead body that heat is generated by chemical action. At a varying interval after death, usually within twelve hours, there is a general contraction and hardening of the muscles due to chemical changes, probably of the nature of coagulation, in them. This begins in the muscles of the head, extends to the extremities, and usually disappears in twenty-four hours. It is always most intense and most rapid in its onset when death is preceded by active muscular exertion.

There have been cases of instantaneous death in battle where the body has remained in the position it held at the moment of death, this being due to the instantaneous onset of muscular rigidity. The blood remains fluid for a time after death and settles in the more dependent parts of the body, producing bluish red mottled discolorations. Later the blood coagulates in the vessels. The body loses moisture by evaporation. Drying of the surface takes place where the epidermis is thin, as over the transparent part of the eye and over areas deprived of epidermis. Decomposition and putrefaction of the body due to bacterial action takes place. The bacteria ever present in the alimentary ca.n.a.l make their way from this into the dead tissue.

Certain of these bacteria produce gas which acc.u.mulates in the tissues and the body often swells enormously. A greenish discoloration appears, which is due to the union of the products of decomposition with the iron in the blood; this is more prominent over the abdomen and appears in lines along the course of the veins. The rapidity with which decomposition takes place varies, and is dependent upon many factors, such as the surrounding temperature, the nutrition of the body at the time of death, the cause of death. It is usually not difficult to recognize that a body is dead. In certain cases, however, the heart's action may be so feeble that no pulse is felt at the wrist, and the current of the expired air may not move a feather held to the nostril or cloud the surface of a mirror by the precipitation of moisture upon it. This condition, combined with unconsciousness and paralysis of all the voluntary muscles, may very closely simulate death. The only absolute evidence of death is given by such changes as loss of body heat, rigor mortis or stiffening of the muscles, coagulation of the blood and decomposition.

CHAPTER III

THE GROWTH OF THE BODY.--GROWTH MORE RAPID IN EMBRYONIC PERIOD.--THE COoRDINATION 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 s.e.x.--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 s.e.xual 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 coordinated, 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 pa.s.s 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 p.u.b.erty, 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 s.e.xual 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 ma.s.s 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.

Haemorrhages 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 ma.s.s, 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 ma.s.s 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 ma.s.s 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.

[Ill.u.s.tration: FIG 14.--PHOTOGRAPH OF A MICROSCOPIC PREPARATION FROM A CANCER OF THE UTERUS. A large ma.s.s of cells is extending into the tissue of the uterus which is shown as the fibrous structure. Such a cell ma.s.s penetrating into the tissue represents the real cancer, the tissue about the cell ma.s.ses 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 pa.s.sage 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 ca.n.a.l 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 coordinated 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 ma.s.s is formed which serves the developing insect for both food and protection. Large tumor-like ma.s.ses 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 a.n.a.logies 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 ma.s.s 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 ma.s.s 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 a.s.sign 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 ma.s.s 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 a.s.sumes 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 pa.s.sing. Every possible resource should be placed at the disposal of the scientific investigation of the subject, for with knowledge will come power to relieve.