Disease and Its Causes

by W. T. Councilman

Chronic Diseases.—Disease Of The Heart As An Example.—The Structure And Function Of The Heart.—The Action Of The Valves.—The Production Of Heart Disease By Infection.—The Conditions Produced In The Valves.—The Manner In Which Disease Of The Valves Interferes With Their Function.—The Compensation Of Injury By Increased Action Of Heart.—The Enlargement Of The Heart.—The Result Of Imperfect Work Of The Heart.—Venous Congestion.—Dropsy.—Chronic Disease Of The Nervous System.—Insanity.—Relation Between Insanity And Criminality.—Alcoholism And Syphilis Frequent Causes Of Insanity.—The Direct And Indirect Causes Of Nervous Diseases.—The Relation Between Social Life And Nervous Diseases.—Functional And Organic Disease.—Neurasthenia.

Chronic diseases are diseases of long duration and which do not tend to result in complete recovery; in certain cases a cause of disease persists in the body producing constant damage, or in the course of disease some organ or organs of the body are damaged beyond the capacity of repair, and the imperfect action of such damaged organs interferes with the harmonious inter-relation of organs and the general well-being of the body. The effect of damage in producing chronic disease may not appear at once, for the great power of adaptation of organs and the exercise of reserve force may for a time render the damage imperceptible; when, however, age or the supervention of further injury diminishes the power of adaptation the condition of disease becomes evident. Chronic disease may be caused by parasites when the relation between host and parasite is not in high degree inimical, as in tuberculosis, gonorrhoea, syphilis, most of the trypanosome diseases and the diseases produced by the higher parasites. In certain cases the chronic disease represents really a series of acute onsets; thus in the case of the parasites there may be periods of complete quiescence of infection but not recovery, the parasites remaining in the body and attacking when the defences of the body are in some way weakened. In such cases there may be temporary immunity produced by each excursion of the disease, but the immunity is not permanent nor is the parasite destroyed. There is a further connection between chronic disease and infection in that the damage to the organs, which is the great factor underlying chronic disease, is so often the result of an infection.

The infectious diseases are those of early life; chronic disease, on the other hand, is most common in the latter third of life. This is due to the fact that in consequence of the general wear of the body this becomes less resistant, less capable of adaptation, and organic injury, which in the younger individual would be in some way compensated for, becomes operative. The territory of chronic disease is so vast that not even a superficial review of the diseases coming under this category can be attempted in the limits of this book, and it will be best to give single examples only, for the same general principles apply to all. One of the best examples is given in chronic disease of the heart.

The heart is a hollow organ forming a part of the blood vascular system and serving to give motion to the blood within the vessels by the contraction of its strong muscular walls. It is essentially a pump, and, as in a pump, the direction which the fluid takes when forced out of its cavity by the contraction of the walls diminishing or closing the cavity space, is determined by valves. The contraction of the heart, which takes place seventy to eighty times in a minute, is automatic and is due to the essential quality of the muscle which composes it. The character, frequency and force of contraction, however, can be influenced by the nervous system and by the direct action of substances upon the heart muscle. The heart is divided by a longitudinal partition into a right and left cavity, and these cavities are divided by transverse septa, with openings in them controlled by valves, each into two chambers termed auricle and ventricle. The auricle and ventricle on each side are completely separated.

The circulation of the blood through the heart is as follows: The blood, which in the veins of the body is flowing towards the heart, passes by two channels, which respectively receive the blood from the upper and lower part of the body, into the right auricle. When this becomes distended it contracts, forcing the blood into the right ventricle; the ventricle then contracts and sends the blood into the arteries of the lungs, the passage of blood into the auricle being prevented by valves which close the opening between auricle and ventricle when the latter contracts upon its contents. When the ventricle empties by its contraction the wall relaxes and the back flow from the artery is prevented by crescentic-shaped valves placed where the artery joins the ventricle. A similar arrangement of valves is on the left side of the heart. The pressure given the blood by the contraction of the right ventricle sends it through the lungs; from these, after it has been oxygenated, it passes into the left auricle, then into the left ventricle and from this into the great artery of the body, the aorta, which gives off branches supplying the capillaries of all parts of the body. Both of the auricles and both of the ventricles contract at the same, time, the ventricular contraction following closely upon the contraction of the auricles. Contraction or systole is followed by a pause or diastole during which the blood flows from the veins into the auricles. The work which the right ventricle accomplishes is very much less than that of the left, and the right ventricle has a correspondingly thinner wall. The size of the heart is influenced by the size and the occupation of the individual being larger in the large individual than in the small, and larger in the active and vigorous than in the inactive. Generally speaking, the heart is about as large as the closed fist of its possessor.

Imperfections of the heart which interfere with its action may be the result of failure of development or disease. An imperfect heart which can, however, fully meet the limited demands made upon it in intra-uterine life, may be incapable of the work placed upon it in extra-uterine life. Children with imperfectly formed hearts may be otherwise perfect at birth, but they have a bluish color due to the imperfect supply of the blood with oxygen, and are known as blue babies. The condition becomes progressively worse due to the progressive demands made upon the heart, and death takes place after some days or months or years, the time depending upon the degree of the imperfection.

Much of the damage of the heart in later life is due to infection. The valves of the heart are a favorite place for attack by certain sorts of bacteria which get into the blood. This is due to the prominent position of the valves which brings them in contact with all the blood in the body, the large extent and unevenness of the surface and to the rubbing together and contact of their edges when closed. At the site of infection there is a slight destruction of tissue and on this the blood clots producing rough wart-like projections. The valves in some cases are to a greater or less extent destroyed, they may become greatly thickened and by the deposit of lime salts converted into hard, stony masses. Essentially two conditions are produced. In one the thickened, unyielding valves project across the openings they should guard, and thus by constricting the opening interfere with the passage of blood either through the heart or from it. In the other the valves are so damaged that they cannot properly close the orifices they guard, and on or after the contraction of the cavities there is back flow or regurgitation of the blood. If, for instance, the orifice of the heart into the aorta is narrowed, then the left ventricle can only accomplish its work of projecting into the aorta a given amount of blood in a given time by contracting with greater force and giving a greater rapidity to the stream passing through the narrow orifice. This the heart can do because, like all other organs of the body, it has a large reserve force which enables it, even suddenly, to meet demands double the usual, and like all other muscles of the body it becomes larger and stronger by increased work. The condition here is much simpler than when the same valve is incapable of perfect closure, or when both obstruction and imperfect closure, are combined as they not infrequently are. In such cases the ventricle must do more than in the first case. It must force through the orifice, which may be narrowed, the amount of blood which is necessary to keep up the pressure within the aorta and give to the circulation the necessary rapidity of flow, and also the amount which flows back into the heart through the imperfectly acting valve. This it can do by contracting with greater force upon a larger amount of blood, the cavity becoming enlarged to receive this. Not only may such damage to the valves be produced, but the muscular tissue of the heart may suffer from defective nutrition or from the effect of poisons, whether these are formed in the body as the effect of disease or introduced from without; or in consequence of disease in the lungs the flow of blood through them may be impeded, or disease elsewhere in the body, as in the kidneys may, by increasing the pressure of the blood within the arteries, throw more than the usual amount of work upon the heart.

The power of the heart in meeting these conditions, however various they are and however variously they act, seems little short of marvellous, and it goes on throwing three and one-third ounces of blood seventy or eighty times a minute into a tube against nine feet of water pressure, working often perfectly under conditions which would be fatal to a machine. As long as this goes on the injury is said to be compensated for; the increased work which the heart is able to accomplish by the exercise of its reserve force and by becoming larger and stronger enables it to cope with the adverse conditions. With increased demand for work there is a gradual diminution of the reserve force. An individual may be able to carry easily forty pounds up a hill and by exerting all his force may carry eighty pounds, but if he habitually carries the eighty pounds, even though the muscles become stronger by exercise the load cannot be again doubled. The dilatation of the heart which is so important in compensation is fraught with danger, because any weakening of the muscle increases the dilatation, until a point is reached when, owing to the dilatation of the orifices between auricles and ventricles, the valves become incompetent to close them.

When the heart is not able to accomplish its work, the effect of the condition becomes apparent by the accumulation of blood within the veins and a less active circulation. This affects the nutrition and the capacity for work of all the organs of the body, and the imperfect function of the organs may in a variety of ways make still greater demands upon an already overloaded heart. Other conditions supervene. The increased pressure within the veins and capillaries due to the impossibility of the blood in the usual amount passing through or from the heart increases the amount of fluid in the tissues. There is always an interchange between the blood within the vessels and the fluid outside of them; the passage of fluid from the vessels is facilitated by the increased pressure within them, just as pressure upon a filtering fluid increases the rapidity of filtration, and the increase of pressure within veins and capillaries impedes passage of tissue fluid into them. The fluid accumulates within the tissues leading to dropsy, or the accumulation may take place in some of the cavities of the body. The diminished flow of blood through the lungs prevents its proper oxygenation; this may also be interfered with by the accumulation of fluid within the air spaces of the lungs.