Duration and Mortality of Phtkisill.—Various circumstances effect the duration of phthisis, as age, sex, constitution, occupation, season of the year, climate, &c. In the upper ranks of life, where patients have all tho advantages that a proper regimen, change of air, and good medical treatment can afford, the average duration of the disease is considerably above that In the lower classes.
The mean duration of 314 cases tabulated by MM. Louis and Bayle was 23 months, Including the extreme cases; hut 162, or more then half of the cases, terminated in nine months, and the greater proportion of them between the fourth and ninth month. By excluding those cases which terminate within four months, and those that exceed four yearst the average duration of the remaining cases is 18 months. With regard to the mortality from phthisis, it varies in different climates, ages, sexes, races, and occupations. In England and Wales, according to the Report of the Registrar-General of Births, Deaths, and Marriages,' it is 20 per cent. of the total number of deaths, or 3.82 annually out of 1000 living. In France it is about the same. On the eastern frontiers of the Cape of Good Hope, where the atmospheric vicissitudes are sudden and great, the thermometer in summer some times varying from 110° to 64, and in winter from to 32°, in the course of a few hours, it is only 31.
In cities the majority of the male labouring population is engaged in the arts, trades, and manufactures, and generally for many hours together in ill-ventilated apartments, and in unhealthy postures of body. In the country the pursuits of the same clasa" of persons are chiefly agricultural. In respect of age, the deaths are greatest between 20 and 30, and diminish gradually to between 50 and 60, after which deaths from phthisis are comparatively unfrequent.
Causes of Pltiltists.—The causes of phtbisis, says Sir T. Clarke, may be divided into "the remote and the exciting, or those which induce the constitutional predisposition, and those which determine the local deposition of tuberculous matter after such predisposition is established. The one class of causes operates by modifying the whole system ; the other, by determining in a system so modified the particular morbid action of which tuberculous matter is the product." Of the remote causes, or those which induce the constitutional predisposition, hereditary transmission is regarded as the most powerful ; not that an individual born of consumptive parents will himself necessarily fall a prey to the same disease, but only that, when exposed to those influences which we are about to enumerate as determining the tuber culous cachexia, he will be more likely to become affected than one born of healthy parents.
At the same time it must be remembered, that with a disease so common as phthisis, a certain number of persona would be descended from phthisical parents who might contract the disease independent of hereditary descent. Dr Walshe, after the examination of 448 cases of disease phthisical and non-phthisical, came to the conclusion that "phthieis in the adult hospital population of this country is, to a slight amount only, a disease demonstrably derived from parents," and it would appear that this is generally true of the middle and upper classes of society in Great Britain.
Whatever may be the real amount of tendency to this disease given by hereditary transmission, there can be no doubt that external circumstances produce a powerful effect. Thus it is found that the death rate from phthisis is much higher for towns than it is for country districts, thus pointing to the fact that the circumstances by which persona are surrounded in towns are more favourable to the development of phthisis than in country districts. Although much may be set down to the wear and tear of a town life as compared with the country, yet when we come to examine the class of persons affected in towns, we are driven to the conclusion that one of the most powerful causes of the development of phthisis is a deficient oxygena tion of the blood. It is found that in London, the deaths from phthisis amongst persons confined in shops is as 2 to 1 compared with the gentry and professional classes. Taking the trades of London, it is found that those which are sedentary favour the development of phthisis much more than those where the occupation is more active. Again, those who work in close and ill-ventilated rooms are more liable to this disease than those who work in more open and better ventilated apartments. In the case of persons who are exposed to the open air, as found by the recent parliamentary inquiry into the state of the barracks for soldiers in London, and nevertheless suffer from pbthisis, it has been discovered that they sleep in close and ill ventilated apartments. The immunity of some districts in Great Britain, as the Hebrides and north-western districts of Scotland, may be attributed to the almost perfect ventilation of the huts or cabins in which the principal part of the population resides. As an illustration of the influence of overcrowding, and the consequent elimination of the oxygenation of the tissues, the following illustration may be given. In the parish of St. James's, Westminster, there are three registration districts ; in one of these 131 persons dwell upon a single acre, in a second 262, and in a third 432 persons live upon an acre. In 1858, the death from phthisis in these districts was as follows : in the first division one person in every 426 died of phthisia; in the second, one in every 44. whilst in the third and most thickly populated district, one in every'327 of the population died. There are however other conditions which lead to the same deficiency of oxygenation in the blood, and which act as occasional predisposing causes of pulmonary consumption. Such are exhausting occupations, inactivity of body, mental depression, insufficient food, and the abuse of spirituous liquors.