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

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.

Every additional burden thrown upon the heart increases the evil. In women the additional burden of pregnancy may suffice to overcome a compensation which has been perfect, and the same may result from an acute attack of disease. Age, diminishing as it does the capacity for work in all organs, diminishes the compensation capacity of the heart, and a heart which at the age of forty acts perfectly may break down at the age of fifty. Compensation may be gained in other ways, as by reducing the demand made upon the heart by changing the mode of life, by leading an inactive rather than an active life, by avoiding excitement or any condition which entails work of the heart. Social conditions are of great importance; it makes a great difference whether the unfortunate possessor of such a heart be a stevedore whose capital lies in the strength of his muscles, or a more fortunately placed member of society for whom the stevedore works and whose occupation or lack of occupation does not interfere with the adjustment of his external relations to the condition of his heart.

Disease of the nervous system does not differ from disease elsewhere. The system is complex in structure and in function. It consists in nerves which are composed of very fine fibrils distributed in all parts of the body and serve the purpose of conduction, and a central body composed of the brain and spinal cord which is largely cellular in character; it receives impressions by means of the nerves and sends out impulses which produce or affect action in all parts. By means of the organs of special sense, the brain receives impressions from the outer world which it transforms into the concepts of consciousness. Many of the impressions which the central nervous system receives from nerves other than those of special sense and even many of the impressions from these and the impulses which it sends out do not affect consciousness. The memory faculty is seated in the brain and all parts of the brain are closely connected by means of small nerve fibres. The nervous system plays an important part in the internal regulation and coordination of all parts of the body, and it is by means of this that the general adjustment of man with his environment is effected.

Malformations of the brain, except very gross conditions which are incompatible with extra-uterine existence, are not very common. At birth those parts of the brain which are the seat of memory and what are understood as the higher faculties are very imperfectly developed. Variations in structure are extremely common, there are differences in different individuals in the nerves and in the number, size, form and arrangement of the nerve cells, and so complex is the structure that considerable variation can exist without detection. The tissue of the central nervous system has a considerable degree of resistance to the action of bacteria, but is, however, very susceptible to injury by means of poisons. Serious injury or destruction of tissue of the brain and spinal cord is never regenerated or repaired, but adjustment to such conditions may be effected by reciprocity of function, other cells taking up the functions of those which were destroyed.

Certain parts of the brain are associated with definite functions; thus, there are areas which influence or control speech and motion of parts as the arm or leg, and there are large areas known as the silent areas whose function we do not know. All activity of the central nervous system, however expressed, is due to cell activity and is associated with consumption of cell material which is renewed in periods of repose and sleep. Fig. 13 shows a nerve cell of a sparrow at the end of a day's activity and the same after the repose of a night.

Diseases of the nervous system have a special interest in that they so often interfere with man in his relations with his fellows. In diseases of other organs the disturbances set up concern the individual only. Thus, others need not be disturbed save by the demands made on their sympathies by an individual with a cold in the head or a cancer of the stomach. Disease of the nervous system is another affair, instead of those reactions and expressions of activity to which we are accustomed and to which society is adjusted, the reactions and activities are unusual and the individual in consequence does not fit into the social state and is said to be anti-social. There are all possible grades of this, from mere unpleasantness in the social relations with such an individual, to states in which he is dangerous to society and must be isolated from it. Insanity is an extreme case. There is no disease signified in the expression, but it is merely a legal term to designate those individuals whose actions are opposed to the social state and who are not responsible for them. In insanity there is falsity in impressions, in conceptions, in judgment, a defective power of will and an uncontrollable violence of emotion. The individual is prevented from thinking the thoughts or feeling the feelings and doing the duties of the social body in the community in which he lives. The insane are out of harmony with their social environment, but not necessarily in opposition to it.

There is no very sharp line between insanity and criminality. The criminal is in direct antagonism to the laws of social life. An insane person may cause the same injury to society as a criminal, but his actions are not voluntary, whereas the criminal is one who can control his actions, but does not. Mentally degenerated persons, however, can be both insane and criminal. Whatever the state of society, this reprobates the actions of one opposed to it; in a society in which it were usual to appropriate the possessions of others or to devour unpleasant or useless relatives, virtue and lack of appetite would be reprobated as unsocial.

The symptoms of insanity or the manner in which the defective action of the brain expresses itself and the various underlying pathological changes vary, and by combining these it has been possible to subdivide insanity into a number of distinct forms. There are both intrinsic and extrinsic causes of insanity. The intrinsic