9 "Die lobuläre pneumonie ist im Sänglingsalter eine ausserordenich häufige Krankheit" (Vogel, Kinderkrankheiten, p. 222).
10 "Lobäre pneumonie kommt viel seltener vor" (Vogel, loc. cit.).
11 Klinik der Kreislaufs u. Athms. org., Breslau, 1856.
In early life, in what may be denominated the first period, anterior to the second year, males and females are very nearly equally affected. Between twenty and forty, the time when the condition of males and females is most diverse, the proportion is 3 males to 1 female, or at least 2 to 1. After sixty, when the hygienic condition of both sexes again differs very slightly, this proportion is less striking, and the disease is pretty evenly divided between old men and old women; still, the male sex always furnishes more cases than the female. When women work as men do, or when both sexes are huddled together (as in prisons), then the difference between them is lost.
The puerperal state does not seem to increase the predisposition, but pneumonia is more apt to occur at the time of the catamenia.
The general condition of the individual at and before the pneumonic seizure seems to have some predisposing influence, although opinion is divided as to whether the strong and robust or the feeble and sickly are the more predisposed to it. Those who are convalescing from acute and severe illnesses, those who are habitual alcohol-drinkers, and those who are under the influence of malarial poison are far more liable to pneumonia than those who are free from such taints. Enervating habits, poverty, antihygienic surroundings and dyscrasiæ (especially cancerous), and chronic nervous diseases act as predisposing causes. Difficult dentition in children seems to act in a similar manner. Diphtheria, erysipelas, measles, small-pox, and other acute infectious diseases must be ranked as causes predisposing to pneumonia.
Chronic and acute uræmia, pyæmia, septicæmia, and all that class of diseases which depend upon the retention of excrementitious substances in the blood, are also powerful predisposing causes. It is also of frequent occurrence in chronic blood diseases, such as chronic alcoholismus. Suppuration in the abdominal cavity, which opens into the thorax, may lead to a pneumonia. Long-continued, passive pulmonary hyperæmia from any cause becomes a predisposing cause to pneumonia. The pneumonia which frequently occurs during acute articular rheumatism has been regarded by some as metastatic from the joints; but the more reasonable explanation is that the blood-changes in rheumatism predispose to pneumonia.
One attack predisposes to others; as many as twenty-eight attacks have been noted in the same individual, the time between the attacks and the number of them being governed by no rule and subject to the widest variations.
When pneumonia follows a severe blow or injury to the chest or shock from any traumatic cause, the injury (or the shock) must be regarded as a predisposing cause. It is noteworthy to observe how often in the aged fracture of the hip-joint is followed by pneumonia. Within four hours after this injury croupous pneumonia has been established.
The influence of prolonged exposure to intense cold and sudden chilling of the surface of the body as a predisposing cause of pneumonia is still undetermined. Cold does not markedly affect the pneumonia-rate, except in the very old. Nearly nine-tenths of the cases of senile pneumonia occur between November and May. The January and February statistics seldom exhibit the highest pneumonia-rate, as they would were there any direct relationship between pneumonia and cold. In elevated regions north-east winds favor the development of pneumonia, and it is most prevalent in any locality during those periods of the year when there are the greatest extremes of temperature. A continuously low or a continuously high temperature has much less influence in its production than great vicissitudes of temperature. In New York City early spring and winter seem to be the periods when it is most prevalent.