Contamination of the atmosphere with emanations the result of the overcrowding of many human beings together, as in prisons, camps, or asylums, especially where decomposition of organic matter is going on, is of great influence in causing diarrhoea. Persons living in badly-ventilated houses, or in houses improperly drained where the air is vitiated by escaping gas from sewer-pipes, are especially prone to be attacked. But sewer-gas, per se, does not cause diarrhoea any more than it causes diphtheria or scarlatina.9 It is a step backward to hang upon this ready explanation all our doubts and our ignorance of the origin of disease. The specific germ of the zymotic diseases may be conveyed in the gases from sewers, but there are other and more direct modes of communication which should receive equal attention.
9 Longstaff (Brit. Med. Journ., London, 1880, vol. i. p. 519) believes that summer diarrhoea has a specific poison which is intimately connected with the process of putrefaction, and that the infective material has its source in the public sewers.
Children are much more liable to intestinal inflammation than adults. This is due to the greater susceptibility of the mucous membrane in them to congestion and catarrh from external influences and from direct irritation. In infants fed upon an unsuitable diet—cow's milk or other substitutes for mother's milk—this susceptibility is much increased. The age most liable to attack is under one year, or from the first to the second year, when, in consequence of dentition, weaning, and a change from a diet chiefly or almost wholly liquid to one of solids, there is a great liability to a disturbance of the normal equilibrium. Intestinal catarrh forms almost one-third of the total number of the affections of childhood. According to the census of 1870, 761 out of every 1000 deaths from diarrhoea, dysentery, and enteritis occurred under the tenth year. In old age a similar predisposition exists, and a mild attack will in old persons induce more serious symptoms than in middle life. Epidemics of diarrhoea among the aged in asylums and hospitals are not uncommon.
Temperament and idiosyncrasy are causes of differences in predisposition. Many persons in consequence of taking cold invariably have diarrhoea, while others as invariably have nasal catarrh or bronchitis. Certain articles of food, as oysters and eggs, lead always in some persons to intestinal disturbance. An exaggerated sensibility of the mucous membrane to particular impressions is the cause of this peculiarity.
Previous attacks of intestinal inflammation render the individual liable to recurrences from very slight causes. The suppression of the menses and of hemorrhoidal discharges and the healing of eruptions are said to be followed by serious diarrhoea, but such an occurrence is probably more often a coincidence than a result.
Sedentary life, by enfeebling muscular movement and by inducing indigestion and constipation, brings on diarrhoea. Constipation impairs the muscular tone of the bowel, and hardened fecal accumulations act as irritants which sometimes provoke acute catarrhal processes—diarrhoea and dysentery. Insufficient clothing in children and in adults makes the skin more susceptible to changes of temperature and conduces to intestinal congestion. Smoking in excess and the use of narcotics and stimulants are mentioned as debilitating causes which pave the way for disease in the intestine; the habitual use of the stronger liquors, by keeping up chronic engorgement of the mucous membrane, is undoubtedly a potent cause. Occupations which involve deprivation of fresh air and sunlight, and all trades which enfeeble the individual, make him liable to all digestive disorders. A feeble constitution, debility from disease, from over-fatigue, or from loss of sleep, or any perturbing influence, puts the body in a state favorable to indigestion and diarrhoea.
The eruptive fevers are accompanied more or less by gastro-enteric catarrh. In scarlet fever, measles, and variola there is a state of equilibrium between the skin and the intestinal mucous membrane. When the morbid manifestation does not normally appear upon the skin there is a transference of irritation to the intestine. The administration of purgatives in the early periods of scarlet fever and measles delays, sometimes prevents, the outburst of the eruption on the skin. The intestinal catarrh of the eruptive fevers has sometimes the significance of an exanthem and sometimes of a secondary complication. In measles it is more frequently the former; in scarlatina and variola it comes later as a complication.
Uræmia, malarial infection, chronic suppuration, pyæmia and septicæmia, cancerous and strumous disease of the mesenteric glands, scurvy, tuberculosis, Bright's disease, and chronic wasting diseases in general, are conditions in which diarrhoea appears as a result of the defective nutrition of the vessels of the intestinal wall and their liability to dilatation and hyperæmia, or from the presence in the blood of septic matter.10
10 For experiments relating to the production of intestinal catarrh by injections of irritating or putrid matter into the blood consult Traité clinique et expérimentelle des Fièvres dites essentielles, Gaspard et Bouillaud; also, Path. anat., Lebert, tome ii., Texte, Paris, 1861, p. 205.
The ingestion of a larger quantity of food than the stomach and intestines are able to soften, and the taking of food essentially indigestible or improperly prepared by cooking, are causes of the passage of masses of food more or less unaltered along the intestinal tract. Hyperæmia follows the mechanical irritation of the mucous surface. When articles of food are in a partial state of putrefaction, so that the antiseptic properties of the gastric juice cannot be quickly enough brought into play, there is a rapid fermentation in the stomach, with the development of symptoms of gastric and subsequently of intestinal catarrh. Unripe fruit, vegetables composed of hard tissue, as early potatoes, cucumbers, pineapples, and cherries, by their indigestible nature, are frequent causes. Oysters, crabs, fish, and lobsters often occasion acute diarrhoea in consequence of being in an unfit condition for food. Cheese has been known to produce violent illness with symptoms of intense intestinal irritation; these effects are due to some poisonous substance, hitherto undiscovered, developed in the course of putrefaction. New coffee causes diarrhoea; six months is usually the time before coffee grown in Ceylon reaches the European and American markets; by this time it does not have this effect.11