Age.—While the disease may occur at any age, fully one-half of the fatal cases are between the ages of 20 and 40. It is less frequent in childhood and in old age. It must be noted, however, that while tubercle of the lungs (con sumption of the lungs) is rare in childhood, tubercular disease of glands is common, and specially of the glands of the belly, causing consumption of the bowels, and tubercular dis ease of the brain (water-in-the-head).
Occupation. —Persons like knife-grinders, miners, stone-masons, &c., exposed to irritating (lust-particles, are frequent victims. The occu pation may lead to exposure, to confined habits of living, to loss of exercise, &c., and so favour the occurrence of the disease. Occupations that compel the body to be kept in constrained posi tions, especially such as hamper the breathing, stooping constantly over a desk, for example, are injurious. On the other hand, occupations compelling active life in the open air increase the natural resistance of the body, and occupa tions that compel active exercise of the lungs, as for instance flute- or other wind-instrument playing. Thus one could speak of a general and a local susceptibility. For instance, a general state of depressed health would make one susceptible to anything, including au attack by the tubercle bacillus, but persons exposed to the breathing of air laden with dust may enjoy perfect general health, while there is increased local susceptibility of the lungs because of the local irritation there. So one can increase the natural resistance of the whole body by active life in the open air, and one could increase, in particular, local resistance to consumption by chest and breathing exercises, as the wind instrument player of necessity does.
Habits and Mode of Living. —Intemper ance and other irregularities of life, and excess of various kinds, by their general effect on the body, are predisposing causes. In a similar way defective nourishment arising from bad or insufficient feeding, or from faulty digestion of one kind or another, has a very powerful influence.
Surroundings.—Breathing an impure atmos phere, such as is common in the small and ill ventilated homes of the poor, too common also in workrooms of tailors and seamstresses, is a very favourable condition for the development of consumption. A damp soil and a moist
atmosphere are also favouring conditions. A variable climate and a cold locality are bad. The value of active exercise and an open-air life has been already referred to.
Hereditary Influence. —Until the infective nature of consumption was fully established, hereditary influence was supposed to be the chief determining cause of consumption. It was a disease which " ran in families," and to have a consumptive father or mother was supposed to ensure that one would develop consumption sooner or later.
It cannot be too emphatically stated that this view must now be aban doned. Consumption is an acquired, not an inherited disease. It is, in deed, in essence, and at first, a local disorder and not a constitutional dis ease, though it may become a general disorder.
It is true that while the real cause —the tubercle organism—of the disease was un known, the facts all seemed to show conclu sively that it was a disease transmitted from parent to child. If one, however, remembers the facts that have been stated, it is easily seen how, no precautions being taken, it would be difficult for children to escape if a father or mother were affected with the disease, and how easy it would be for one child to infect another. These facts show that what was for a long time believed to be a family tendency is as easily accounted for on the infection view. The same facts indicate the means by which, if one member of the family becomes attacked, the other members may be protected. These means will include the separation, altogether if possible, of the infected member of the family. If complete separation is impossible, the adop tion of precautions, such as a separate room for the infected person, the use of disinfectants, the disinfection of the spit, &c., will go far to prevent infection of the others.
It is impossible in a work like this to go into detail in the way of showing the proof of the facts that have been stated. It is only possible to note without qualification the practically accepted views that now prevail. But how difficult it may be to distinguish between an inherited disease and an acquired one may be illustrated in consumption.