Disease and Its Causes by William Thomas Councilman (early reader books .TXT) 📕

Several of the organs of the body, in addition to the formation of secretions which are discharged on the surfaces by means of their ducts, produce also substances which pass directly into the blood or lymph, and have an influence in stimulating or otherwise regulating the activity of other organs. There are also certain organs of glandular structure which are called the ductless glands; these are not connected with the surface and all their secretion passes into the blood. It is a part of recent knowledge that the substances produced in these glands are of great importance for the body, some of them even essential for the maintenance of life. In front of the neck is such an organ, the thyroid gland (Fig. 8, 14). Imperfect development or absence of this organ, or an inactive condition of it, produces in the child arrested growth and deficient mental development known as cretinism, and in the adult the same condition gives rise to mental deterioration, swelling of the skin, due to a greater content of water, and loss of hair. This deficiency in the production of thyroid secretion can be made good and the symptoms removed by feeding the patient with similar glands removed from animals. The very complex disease known as exophthalmic goitre, and shown by irregular and rapid action of the heart, protruding eyeballs and a variety of mental symptoms, is also associated with this gland, and occasioned not by a deficiency but by an excess or perversion of its secretion.

Adjoining the thyroid there are four small glands, the parathyroids, each about the size of a split pea. The removal of these glands in animals produces a condition resembling acute poisoning accompanied by spasmodic contraction of the muscles. A small glandular organ at the base of the brain, the pituitary body, produces a secretion, one of the most marked properties of which is a control of growth, particularly that of the bones. Most cases of giantism, combined as they are with imperfect mentality, are due to disease of this gland. There are glands near the kidney which regulate the pressure of the blood in the arteries by causing contraction of their muscular walls. The sexual characteristics in the male and female are due to an internal secretion produced by the respective sexual glands which affects growth, body development and mentality.

So is the body constituted. A series of surfaces, all connected, of enormous size, which enclose a large number of organs and tissues, the activities of which differ, but all are coördinated to serve the purposes of the organism as a whole. We should think of the body not as an assemblage of more or less independent entities, but as a single organism in which all parts are firmly knit together both in structure and in function, as are the components of a single cell.

No Sharp Line Of Demarkation Between Health And Disease.—The Functional Nutritive And Formative Activities Of Cells.—Destruction And Repair Constant Processes In Living Matter.—Injuries To The Body.—The Effect Of Heat.—The Action Of Poisons.—The Lesions Of Disease.—Repair.—The Laws Governing Repair.—Relation Of Repair To Complexity Of Structure And Age.—The Reserve Force Of The Body.— Compensatory Processes In The Body.—Old Age.—The Diminution Of Resistance To The Effect Of The Environment A Prominent Factor In Old Age.—Death.—How Brought About.—Changes In The Body After Death.— The Recognition Of Death.

There is no sharp line separating health from disease; changes in the tissues of the same nature, or closely akin to those which are found in disease, are constantly occurring in a state of health. The importance of parasites in causing disease has led to the conception of disease as almost synonymous with parasitism; but it must be remembered that the presence of parasites living at the expense of the body is perfectly consistent with a state of health. Degeneration, decay and parasitism only become disease factors when the conditions produced by them interfere with the life which is the normal or usual for the individual concerned.

All the changes which take place in the cells are of great importance in conditions of both health and disease, for life consists in coördinated cell activity. The activities of the cells can be divided into those which are nutritive, those which are functional and those which are formative. In the functional activity the cell gives off energy, this loss being made good by the receipt of new energy in the form of nutritive material with which the cell renews itself. In certain cells an exact balance seems to be maintained, but in those cells whose activity is periodic function takes place at the expense of the cell substance, the loss being restored by nutrition during the period of repose. This is shown particularly well in the case of the nerve cells (Fig. 13). Both the functional and nutritive activity can be greatly stimulated, but they must balance; otherwise the condition is that of disease.

Fig. 13—Nerve Cells Of An English Sparrow (a) Cells after a day's full activity, (b) cells after a night's repose In (a) the cells and nuclei are shrunken and the smaller clear spaces in the cells are smaller and less evident than in (b). (Hodge)

Fig. 13—Nerve Cells Of An English Sparrow (a) Cells after a day's full activity, (b) cells after a night's repose In (a) the cells and nuclei are shrunken and the smaller clear spaces in the cells are smaller and less evident than in (b). (Hodge)

The formative activity of cells is also essential to the normal state. Destruction of cells is constantly taking place in the body, and more rapidly in certain tissues than in others. Dried and dead cells are constantly and in great numbers thrown off from the surface of the skin: such epidermic appendages as the hair and nails grow and are removed, millions of cells are represented in the beard which is daily removed. Cells are constantly being destroyed on the intestinal surface and in the glands. There is an enormous destruction of the blood cells constantly taking place, certain essential pigments, as that of the bile, being formed from the hæmoglobin which the red blood corpuscles contain and which becomes available on their destruction. All such loss of cells must be made good by the formation of new ones and, as in the case of the nutritive and functional activity, the loss and renewal must balance. The formative activity of cells is of great importance, for it is by means of this that wounds heal and diseases are recovered from. This constant destruction and renewal of the body is well known, and it is no doubt this which has given rise to the belief, widely held, that the body renews itself in seven years and that the changes impressed upon it by vaccination endure for this period only. The truth is that the destruction and renewal of most tissues in the body takes place in a much shorter interval, and, as we shall see, this has nothing to do with the changes concerned in vaccination. All these activities of the cells vary in different individuals, in different parts and at different ages.

The lesions or injuries of the body which form so prominent a part of disease vary in kind, degree and situation, depending upon the character of the injurious agent, the duration of its action and the character of the tissue affected. The most obvious injuries are those produced by violence. By a cut, blood vessels are severed, the relations of tissues disturbed, and at the gaping edges of the wound the tissue usually protected by the skin is exposed to the air, resulting in destruction of the cells contained in a thin layer of the surface. The discoloration and swelling of the skin following a blow is due to rupture of vessels and escape of blood and fluid, and further injury may result from the interruption of the circulation.

By the application of heat the tissue may be charred and the albumen of the blood and tissue fluids coagulated. Living cells are very susceptible to the action of heat, a temperature of 130 degrees being the thermal death point, and even lower temperatures are fatal when their action is prolonged. The action of the heat may produce definite coagulation of the fluid within the cells in the same way that the white of an egg is coagulated. Certain of the albumens of the body coagulate at a much lower temperature than the white of the egg (as the myosin, one of the albumens of the muscle which coagulates at 115° F., egg white coagulating at 158° F.), and in addition to such coagulation or without it the ferments within the cell and to the action of which cellular activity is due may be destroyed.

In diseases due to parasites, the parasite produces a change in the tissue in its immediate vicinity often so great as to result in the death of the cells. The most general direct cause of lesions is toxic or poisonous substances, either introduced from without or formed in the body. In the case of the parasitic diseases the mere presence of the parasite in the body produces little or no harm, the injury being caused by poisons which it produces, and which act both locally in the vicinity of the parasite and at a distance, being absorbed and entering the blood stream. How certain of the poisonous substances act is easy to see. Strong caustics act by coagulating the albumen, or by the withdrawal of water from the cell. Other poisons act by forming stable chemical compounds with certain of the cell constituents and thereby preventing the usual chemical processes from taking place. Death from the inhalation of illuminating gas is due to the carbon monoxide contained in this, forming a firm chemical union with the hæmoglobin of the red corpuscles so that the function of these as oxygen carriers is stopped.

In order that most poisons may act, it is essential that they enter into the cell, and they cannot do this unless they are able to combine chemically with certain of the cell constituents. To this is due the selective action of many poisons. Morphine, for example, acts chiefly on the cells of the brain; strychnine acts on the cells of the spinal cord which excite motion and thus causes the characteristic muscular spasm. The poisonous substances produced by bacteria, as in the case of diphtheria, act on certain of the organs only. Different animal species owe their immunity to certain poisons to their cells being so constituted that a poison cannot gain entrance into them; pigeons, for example, cannot be poisoned by morphia. Individual variations play an important part also; thus, shellfish are poisonous for certain individuals and not so for others. Owing to the variability of living structures a substance may be poisonous at one time and not at another, as the following example shows. A man, very fond of crab meat, was once violently poisoned after eating crabs, being at that time seemingly in his usual state of health, and no illness resulted in others who had partaken of the same crabs. Two months later a hearty meal of crabs produced no ill result. There are also individuals so constituted that so simple a food as the egg is for them an active poison.

The lesions produced by the action of injurious conditions are usually so distinctive in situation and character that by the examination of the body after death the cause of death can be ascertained. The lesions of diseases may be very obvious to the naked eye, or in other cases only the most careful microscopic examination can detect even the presence of alterations. In the case of poisons the capacity of the cell for adaptation to unusual conditions is of great importance. It is probable that certain changes take place within the cells, owing to which the function can be continued in