Definition:—A condition of general systemic or local infection from the presence of a specific micro-organism, the bacillus tuberculosis, characterized by the development at the point or points of lodgment of the bacilli, of gray or grayish white, pearl-like or perhaps yellowish nodular bodies, or tubercles—elementary masses. These, aggregating, form larger tubercular masses, which in turn pass through the processes of caseation, sclerosis, ulceration and tissue necrosis, or in an occasional case, they become calcified.
Etiology:—The true and unquestioned cause of this disease, the bacillus tuberculosis, was discovered by Koch in 1881. This at once established the fact that the inflammatory processes were not the cause of the formation of tuber-cules, but that these processes were the result of tuberculous development.
There are many predisposing causes, but the fact that there must be constitutional weakness—a condition of the system, or of the tissues favorable to the growth and development of the germ—must not be forgotten. A favorable constitutional condition may result from the presence of an hereditary weakness, or dyscrasia, or vital impairment, or it may be entirely the result of environment. Nationality has a strong predisposing influence. The negroes and the American Indians in our own country, and any crosses between them and the white race, are very susceptible to the development of the disease. Some other races are also quite subject to it. With Irish immigrants in the United States the mortality is next to that of the colored races. In the north and in the mountainous regions—in high altitudes—there is a degree of exemption from its ravages. Where there is prolonged moisture and cloudy weather, with abrupt temperature changes, in low altitudes, it is more prevalent. It is more common also in crowded portions of large cities. Children born in unsanitary surroundings, of parents who are habitually dissipated or who suffer from syphilis or other constitutional dyscrasia, especially those who have had tuberculosis, are liable to its infection.
The theory that the disease is hereditarily transmitted, as generally considered, is now discarded, but the constitutional weaknesses induced by the disease—a lack of resisting power—is certainly entailed, and children so encumbered are especially liable to tuberculosis. There may be hereditary transmissions, from the mother to the child, in utero, by direct infection. The disease may at once appear in the child, or after a varying period of incubation, it may appear in childhood or in early adult life, take on active development, either locally or in a constitutional form, and result fatally.
Those conditions which are named as inducing pneumo-nokoniosis—the inhalation of different forms of dust—will predispose the respiratory passages to direct infection, or will induce conditions which, lowering the vitality, will permit the invasion of the disease.
The germs are usually introduced through the inhalation of dried impalpable dust, which carries them into the respiratory passages. It is argued that the exhalations of tubercular patients are not likely to carry the infection, as these are moist and in masses, although Flügge argued strongly that the germ is carried in very minute droplets, or minutely subdivided particles of sputum and saliva directly by coughing from the infected patient to the individual. The exhalations expectorated and dried, finally become pulverized and then float in the atmosphere. Unlike acute contagious diseases it is not conveyed by a single exposure, but the prolonged immediate association with the patient is necessary to induce infection. The walls of the house or room in which the patient lives, with its contents, will in time become infected with the germs, which may persist for months in spite of energetic measures to destroy them, and one continually occupying the room, subsequently will be liable to infection.
The ingestion of food which contains the tubercle bacilli is the cause of the disease. The milk from tuberculous cows or the meat of diseased animals is a direct cause of infection. Koch in 1901 discarded the idea that tuberculosis in domestic animals and that of man were identical, and claimed that man was not susceptible to infection from cows. This statement was not accepted at the time, and observations made since have served to disprove it. The belief now is that while the germ in animals differs somewhat from that in man, the results of its influence in man are the same with both.
Tuberculosis will follow immediately as the sequel of certain acute infectious diseases. It is not uncommon after a protracted case of influenza, pneumonia, whooping cough, cirrhosis of the lungs or other severe lung disease or after typhoid fever or the exanthematous diseases, especially measles. It is an accompaniment of the later stages of diabetes.
In childhood this disease manifests itself more frequently in a local form. In early life, however, there may be pulmonary manifestations, but these are not apt to occur before the age of eighteen years. From that time until thirty the pulmonary form is much more common than at any other age. It seldom develops after middle life, and if it should occur in childhood its course is very rapid. Intestinal tuberculosis, tuberculosis of the bones, of the skin, of the lymphatic glands, and of the meninges are more common in childhood.
Tuberculosis occurs with but little more frequency in females than in males. Young married women who have the essential conditions for the development of the disease will find that it develops during the first pregnancy. It may not persist, however, but may be apparently controlled. It is liable to remain latent until a subsequent pregnancy, when it will show rapid development and may prove fatal in a short time after confinement.