CONSUMPTION (TUBERCULAR DISEASE OF THE LUNGS).
Consumption is now recognized as a disease due to infection by an organism, the tubercle bacillus (see p. 501). The organism can be found in the spit of consumptive patients, can be isolated from it, can be grown apart from other organisms, and the pure culture of the organism thus obtained will reproduce the dis ease if introduced into the body of man or animal. See Plate XXI.
The opportunities of infection must be ex tremely numerous. One has only to consider the large number of persons suffering from consumption and the myriads of the organisms expelled from their bodies in the spit from the lungs, which when the spit dries may be every where disseminated in the air in dust, to per ceive that wherever there is a crowded popu lation the chances of infection must be many. It has been calculated that one consumptive patient may discharge in the spit 20 millions of bacilli daily. The presence of living viru lent organisms in dust has been clearly proved by experiment. In England and Wales the death-rate from consumption in the years 1891 to 1894 was 15 for every 10,000 living. But in London alone, between the years 1897 and 1899, the proportion of deaths from all kinds of tubercular disease, between the ages of 20 and 25 years, was over 40 per cent. But about 38 of that 40 per cent was due to tubercular disease of the lungs alone. Although these facts do not apply to the same years, neverthe less they illustrate how density of population affects the amount of the disease.
There is a quite conclusive amount of facts of this and other kinds to show that man him self is the chief agent in disseminating the in fection, and that be does this by the spit from diseased lungs. There are, however, other sources of infection, chiefly meat and milk.
Tubercular disease is widely prevalent among animals—cattle, rabbits, monkeys, guinea-pigs, —but specially so aiming domesticated animals. The milk of cows affected by tubercular dis ease in any part of the body is infective, and so also is the flesh of tubercular animals. The identity, however, of tubercular disease of cattle and that of man has been lately denied by Koch, one of the greatest authorities on the subject. This part of the question, however, is still under investigation, and the only safe view is that tubercle in man and animals is the same, and that the meat and milk of tuber cular animals is a source of human infection.
It is certain, however, that the organism is destroyed by a temperature considerably below that of boiling-point, and that proper cooking of the meat, and beating milk to a point just below that of boiling, will destroy any infective quality.
The opportunities of infection, then, specially in crowded towns, are numerous. Why is the disease not even more wide-spread than it is? This is partly due to the fact that the tubercle bacillus flourishes within a comparatively nar row range of temperature, between 80° and 108° F., and does not therefore multiply out side the body ; direct sunlight destroys them in a few minutes; and ordinary daylight and fresh air are destructive to them.
If, then, consumptive patients were univer sally to cease expectorating carelessly anywhere, and were constantly to use spit-bottles or flasks which were regularly disinfected, if the meat of tubercular cattle were rigorously destroyed, if it became the universal practice to heat milk before use, if town and county authorities were to insist on air-spaces being strictly maintained between dwellings, and were to secure the abolition of back-lands, of ill-lighted and ill ventilated tenements, workships, and factories, this disease might soon become as rare as small pox. It has, indeed, already been shown that a considerable decline has of recent years taken place in the deaths from consumption, due to the improved sanitary conditions in which the people live.
Individual Susceptibility to Consump is still another element to be considered in answering the question why con sumption, considering the chances of infection, is not even more frequent than it is ; that ele ment is the natural resistance of the body to the disease. This natural resistance will vary, not only in different individuals, but also in the same individual at different times. To put it in other words, one person is more susceptible than another. The susceptibility will vary, as it does in other diseases, with temperament, type of constitution, with habits, occupation, and so on; and in the same individual the sus ceptibility will vary from time to time as the general vigour and robustness of the person varies. The chief circumstances that affect susceptibility come under the following heads.