12 United States Sanitary Commission's Memoirs—Medical, p. 600, New York, 1867.
From the foregoing sketch of its history it is evident that typhus fever has prevailed from time to time in almost all the countries of Europe. Indeed, it is probable that no one of them has wholly escaped its ravages, while in others—as, for example, Ireland—it has been more or less constantly present until within the last few years, when its visitations have been less frequent as well as less severe. Even in countries which are popularly supposed to enjoy an immunity from it there is evidence of an incontrovertible character that it has occasionally occurred. Such an immunity has been claimed for France, but in the works of Riverius,13 Ambrose Paré,14 and others will be found descriptions of the disease which leave no doubt upon the mind of their entire familiarity with it; and Hirsch, in his work on Historico-Geographical Pathology, is able to give references to several writers who describe outbreaks that have recently occurred there. The disease has also been observed in Iceland. Typhus fever is of much less frequent occurrence in the other divisions of the eastern hemisphere than in Europe. According to Murchison, there are no authentic records of its having been met in Africa, or, with the exception of India, in Asia, such as it is seen in England and Ireland. There are, however, reports of its occurrence in Asia Minor, Syria, Persia, Egypt, Nubia, Tunis, and Algeria, which Hirsch,15 on the other hand, believes place the occasional presence of this disease in these countries beyond doubt. The same difference of opinion exists between these two distinguished observers in regard to the accounts which have been published of typhus fever occurring in Mexico, Central America, and South America, the latter holding that they are entirely reliable, the former that the cases described in them were really cases of malarial or typhoid fever. The disease has never been met with on the continent of Australia, in New Zealand, or in the valley of the Mississippi and the States bordering on the Pacific Ocean in our own country.
13 The Practice of Physick, being chiefly a Translation of the Works of Lazarus Riverius, London, 1678.
14 Traité de la Peste, de la Petite Verolle et Rougeolle, par Ambrose Paré, Paris, 1568.
15 Loc. cit.
While Hirsch's researches go to show that the tropical zone has not been so wholly exempt from the visitation of typhus fever as some authors have asserted, they establish the fact that it is of much less frequent occurrence there than in the colder portions of the temperate zone, where the modes of life are certainly much more favorable to its extension. Natives of warm climates are as liable to be attacked by it as others upon coming to places where it is prevailing, and in the Philadelphia epidemic of 1836, which Gerhard16 has described, negroes and mulattoes suffered from it more severely than the whites.
16 Loc. cit.
ETIOLOGY.—The etiology of typhus fever will be best studied under the heads Predisposing and Exciting Causes.
PREDISPOSING CAUSES.—It may be stated, generally, that whatever impairs the health or reduces the strength of an individual, even temporarily, or acts depressingly on his nervous system, predisposes him to typhus fever. But there are among the predisposing causes some which exert a more special influence on its production than others. Among the more powerful of these is the overcrowding of human beings, with deficient ventilation. Indeed, there are some authors who consider that this has been in many cases alone sufficient to occasion the disease; and although this opinion, as it involves the admission that it may be generated de novo, is contested by others, there is great unanimity among authors in attaching great importance to it. Of the patients admitted into the London Fever Hospital with typhus fever, a large proportion came from the more crowded districts of the city. The disease has always been most prevalent in the poorer quarters of Glasgow, Dublin, and Edinburgh, and when epidemic in Philadelphia in 1836 it was confined to a portion of the town which has always been noted for the squalor and misery of its inhabitants. Among those admitted during that year to the Philadelphia Hospital were seven negroes, said by Gerhard to be "the entire population of a cellar." It is probably largely due to the fact that the better social condition of the poor in this country prevents the degree of crowding which often exists in European cities that the disease is comparatively rare here. The effect of overcrowding is of course much increased by want of cleanliness, either of the person or of the clothes.
Poverty, not merely from its own depressing influences, but also from the fact that it leads to overcrowding, is a powerful predisposing cause of typhus fever. Insufficiency of food, which is one of its many consequences, by impairing his nutrition and thus diminishing his vital resistance, renders the individual more susceptible to the action of the specific cause. Gerhard says that of the patients seen by him in 1836 a very small proportion came from the better class of mechanics, and Tweedie17 and Sir William Jenner18 state that it is rare to meet with instances of the disease, except in the case of medical practitioners and students, among those in comfortable circumstances. Bateman19 goes so far as to assert that "deficiency of nutriment is the principal source of epidemic fever;" and there is certainly a remarkable coincidence in time between outbreaks of this fever and seasons of want and distress. But, as Murchison has shown, destitution is not essential to the production of typhus, for the Dundee epidemic of 1865 was due to overcrowding of the town, brought about by the inhabitants of the surrounding country flocking into it in consequence of labor being unusually abundant and wages good.