17 Lectures on the Distinctive Character, Pathology, and Treatment of Continued Fevers, by Alexander Tweedie, M.D., F.R.S., London, 1842; and Clinical Reports on Fever, by same author, London, 1830.
18 On the Identity or Non-Identity of Typhoid and Typhus Fevers, by William Jenner, M.D., London, 1880; also Lancet, November 15, 1879.
19 A Succinct Account of Typhus or Contagious Fever of this Country, by Thomas Bateman, M.D., F.R.S., London, 1820.
Similar in its action to the above cause is intemperance. Not only is the habitual drunkard more likely to suffer from typhus fever than the temperate man, but a single debauch has been followed by an attack in individuals who had previously resisted the contagion. On the other hand, the most rigid temperance will not afford in all cases a complete immunity from its effects. The debility left by an illness is also a condition favoring the occurrence of an attack of the disease in those who are exposed to its exciting cause. Fatigue of all kinds renders the body less able to resist the causes of disease, and typhus fever is not an exception to the general rule. Overworked nurses are specially liable to contract it. The depressing emotions also favor its occurrence. It has been observed during epidemics that those who exhibit an excessive fear of the contagion are much more likely to suffer from it than the cheerful and courageous.
No age enjoys an immunity from the disease. In fact, it is probable that all ages are equally liable to it. Buchanan20 has seen it at the London Fever Hospital in an infant a fortnight old and in a man of eighty, and attributes the prevailing opinion that children rarely suffer from it to the fact that they are not often taken to hospitals, but are retained in their own homes for treatment. Gerhard21 says that no children in the asylum attached to the Philadelphia Hospital were attacked with the disease during the prevalence of the epidemic there, but the distance of the asylum from the wards in which the cases were treated was probably the reason of their escaping. In the few cases which have come under my own observation the patients were young men, varying in age from twenty-five to thirty-five. The sexes also suffer from it equally. In some epidemics there may be a preponderance of one sex over the other, but in others the reverse has been the case.
20 A System of Medicine, edited by J. Russell Reynolds, M.D., F.R.C.P., etc., vol. i., article "Typhus Fever," London, 1866.
21 Loc. cit.
Occupation, except so far as it brings the individual into immediate contact with the sick, as in the case of physicians, nurses, and clergymen, does not predispose to the disease. There would seem also to be no difference in the susceptibility of the different races to the contagion. Acclimatization affords no protection from the disease, as it does in the case of typhoid fever, and change of the habits of life does not appear to exercise any influence upon the liability to it. On the other hand, the susceptibility of different individuals, and of the same individual at different times, varies considerably. Thus, while in many persons a single exposure to the contagion is followed by an attack, in the case of an engineer mentioned by Murchison it did not occur until after fifteen years of continuous service at the London Fever Hospital. A person who has once suffered from typhus fever is not likely to contract it again, but this protection is not complete, as there are a few well-attested instances of a second attack on record.
The disease prevails most frequently during the winter and early spring, principally because the cold weather of these seasons leads to the closing of windows and all other avenues of ventilation, thus intensifying its exciting cause. Still, some epidemics of great severity have occurred in the warmer months of the year, as, for instance, the one described by Gerhard. It is also doubtful if there is any relation between variations in temperature and the amount of moisture in the air and the prevalence of epidemics of typhus fever, although Hirsch regards a low and damp situation as powerfully predisposing to the endemic and epidemic prevalence of the disease. It is usually met with in towns on the sea-coast or on navigable rivers, but it has also been observed frequently in country districts, and even in regions at a considerable elevation above the level of the sea.
EXCITING CAUSE.—The principal if not the only exciting cause of typhus fever is a specific contagion developed in the bodies of the infected and transmitted from them to the healthy by actual contact, by fomites, or through the atmosphere. The nature of this contagion is unknown. A careful study of its peculiarities seems to justify the opinion that it depends upon the presence of a minute organism in the emanations given off by the sick, which is capable of indefinitely multiplying itself in the human body. But this is only an hypothesis, which rests principally upon the analogy between typhus and some other diseases, as, for instance, relapsing fever and diphtheria, in which such a growth is thought to have been discovered, and upon the fact that the contagious principle whatever it may be, is destroyed by a temperature over 204° F.