Infections : Part 2

Disease and its Causes
by William Thomas Councilman, M.D.

(Page 9 of 16)

The primary seat of the infection in man is generally in the upper part of the lung. The organisms settle on the surface here and cause multiplication of the cells and an inflammatory exudate in a small area. With the continuous growth of the bacilli in the focus, adjoining areas of the lung become affected, and there is further extension in the immediate vicinity by means of the lymphatics. Small nodules are formed and larger areas by their coalescence. Infection with tuberculosis is so common that at least three-fourths of all individuals over forty show evidences of it. The examination of two hundred and twenty-five children of the average age of five years who had died of diphtheria showed tuberculous infection in one-fifth of the cases and the frequency of infection increases with age. The defence on the part of the body is chiefly by the formation of dense masses of cicatricial tissue which walls off the affected area and in which the bacilli do not find favorable conditions for growth. This mode of defence, which is probably combined with the production of substances antagonistic to the toxines produced by the bacilli, is so efficacious that in the great majority of cases no further extension of the process takes place.

In certain cases, however, the growth of the bacilli in the focus is unchecked, the tissue about them is killed and becomes converted into a soft semi-fluid material; further extension then takes place. All parts of the enormous surface of the lungs are connected by means of the system of air tubes or bronchi, and the bacilli have favorable opportunity for distribution, which is facilitated by sudden movements of the air currents in the lung produced by coughing. The defence of the body can still keep pace with the attack, and even in an advanced stage the infection can be checked in some cases permanently; in others the check is but temporary, the process of softening continues, and large cavities are produced by the destruction of the tissue. On the inner surface of these cavities there may be a rapid growth of bacilli.

From the lungs the bacilli are carried by the lymphatics to the lymph nodes at the root of the lungs, in which a similar process takes place; this, on the whole, is favorable, because further extension by this route is for a time blocked. The extension by means of surfaces continues, the abundant sputum which is formed in the lungs and which contains large numbers of bacilli, becomes the vehicle of transportation. The windpipe and larynx may become infected, the back parts of each are more closely in contact with the sputum and are the parts most generally infected. A large part of the sputum is swallowed and infection of the intestine takes place, the lesions taking the form of large ulcers. From the intestinal ulcers there is further extension by means of the lymphatics, to the large lymph nodes in the back of the abdominal cavity; the bacilli may also pass from the ulcers into the abdominal cavity and be distributed over the surface of the peritoneum resulting in tuberculous peritonitis. When the disease has reached an advanced stage, bacilli in small numbers continually pass into the blood and are distributed by this over the body, producing small nodules in many places. In rare cases distribution by the blood is the principal method of extension, and immense numbers of small foci of disease are produced, the form of disease being known as acute miliary tuberculosis.

Although the bacilli are distributed everywhere, certain organs, as the brain and muscles, are usually exempt, because in these the conditions are not favorable to further growth of the bacilli. Tuberculosis, although frequently a very acute disease, is usually one of the best types of a chronic disease and may last for many years. The chronic form is characterized by periods of slow or rapid advance when conditions arise in the body favorable for the growth of the bacilli, and periods when the disease is checked and quiescent, the defensive forces of the body having gained the upper hand. Often the intervention of some other disease so weakens the defences of the body that the bacilli again find their opportunity. Thus typhoid fever, scarlet fever and other diseases may be followed by a rapidly fatal advance of the tuberculosis, starting from some old and quiescent focus of the disease.

Tuberculosis is also one of the best examples of what is known as latent infection. In this the infectious organisms enter the body and produce primary lesions in which the organisms persist but do not extend owing to their being enclosed in a dense and resistant tissue, or to the production of a local immunity to their action. Dr. Head has recently examined the children of households in which there was open tuberculosis in some member of the household. By open tuberculosis is understood a case from which bacilli are being discharged. He found with scarcely an exception that all the children in such families showed evidences of infection. The detection of slight degrees of tuberculous infection is now made easy by certain skin reactions on inoculation of the skin with a substance derived from the tubercle bacilli. Such latent infections may never become active and in the majority of cases do not. When, however, in consequence of some intercurrent disease or conditions of malnutrition the general defences of the body become weakened extension follows. Such latent infections explain the enormous frequency of tuberculosis in prisons. Under the general prison conditions infection in the prisons probably does not take place to any extent, and the disease is as common when the prisoners are kept in individual cells as in common prisons. It is probable that in these cases the prisoners have latent tuberculosis when entering, and the disease becomes active under the moral and physical depression which prison life entails.

For the extension of infection from one individual to another the infecting organisms must in some way be transferred. The most important of the conditions influencing this are the localization of the disease and the character of the infectious organisms, particularly with regard to their resistance to the conditions met with outside of the body. The seat of disease influences the discharge of organisms; thus, if the disease involve any of the surfaces the organisms become mingled with the secretions of the surface and are discharged with these. If the seat of disease be in the lungs, the throat or the mouth, the sputum forms the medium of extension, which can take place in many ways. The sputum may become dried, forms part of the dust and the organisms enter with the inspired air. The organisms which cause most of the diseases in which the sputum becomes infectious are quickly destroyed by conditions in the open, such as the sunlight and drying; street dust does not play so prominent a part in extension as is generally supposed. Organisms find much more favorable conditions within houses. It is now generally recognized that infection with tuberculosis does not take place in the open, but in houses in which the bacilli on being discharged are not destroyed. The hands, the clothing and surroundings even with the exercise of the greatest care may become soiled with the saliva.

New York, Henry Holt And Company.
London, Williams and Norgate, originally published 1913