Similar testimony might be adduced from a large part of Africa, much of Asia, the Indian Archipelago, and the West Indies. It rages "murderously" in Peru, causing a mortality in some epidemics of 60 to 80 per cent., and occurs in this country not only in the valleys, but in cities and provinces at the lofty elevation of 8000 to 13,000 feet.
Heat, moisture, vegetable decomposition, and sudden atmospheric change are the distinguishing characteristics of southern climes, and the study of the etiology of a disease incident or indigenous to these conditions calls for an investigation of these various factors.
It is well established of dysentery that it occurs for the most part in the hottest season of the year. Of 546 epidemics tabulated by Hirsch, 404 prevailed in summer and fall, 113 in fall and winter, 16 in spring and summer, and only 13 in winter. Fourteen-fifteenths of the whole number of epidemics occurred in the months of June to September. And it is corroborative of these conclusions that of 1500 deaths from dysentery in the cities of Boston, New York, Philadelphia, and Baltimore from 1816 to 1827, 1100 occurred in the months of July, August, and September. In fact, the Census Reports (1860-70) of our country show the maximum mortality in August and September, and the minimum in January and February.
The prevalence of unusual heat may also call out an epidemic in places where the disease usually shows itself only in endemic or sporadic form. Thus, the severe epidemic of 1540 in England was preceded by a heat so intense as to dry up the wells and small streams, in consequence of which many cattle died of thirst; and the epidemics of 1583 in Germany, of 1758 in France, and of 1847 in our own country, were characterized in the same way. Interesting in this connection is the statement of Frick concerning the epidemic in Baltimore in 1849, who found the cases to increase and decrease almost in proportion to the elevation and depression of temperature. The epidemic of Weimar in 1868, where 12,000 people fell ill with the disease, illustrated the rule when it ceased suddenly on the approach of cool weather at the end of August.
But that heat alone is not sufficient to account for the genesis of the disease is apparent from the occasional occurrence of it in the tropics in the colder seasons of the year; in the colder climates, Russia, Sweden, and Canada; and in temperate regions during exceptionally cool seasons, as in Plymouth in 1769, London in 1808, Massachusetts in 1817. Moreover, the temperate zone is often characterized by seasons of unusual heat, during the prevalence of which dysentery may be almost unknown. Thus, during the summer of 1881, in Cincinnati, the thermometer scarcely fell below 95° F. for weeks at a time, and was often nearly 100° during the entire night, but the records at the Health Office show that while cases of heatstroke were alarmingly frequent, dysentery was unusually rare during the entire season.
That moisture cannot act more, at most, than as an occasional predisposing cause of dysentery is sufficiently clear from the statement of Hirsch, that of 119 epidemics, 62 commenced or were preceded by wet and 57 by dry weather. In truth, dryness long continued and excessive heat have already been invoked as remote causes of the disease. But moisture, as contributing to, or being a necessary element of, vegetable decomposition, the third characteristic of tropical regions, is entitled to further consideration. Annesley observed that among troops stationed in the vicinity of rivers, canals, and places abounding with emanations from the decay of animal and vegetable matters dysentery became extremely prevalent and assumed a more or less malignant nature; and Baly, who studied the disease in its famous outbreak in the Milbank Penitentiary, remarks that "it is greatest at those seasons and in those states of the atmosphere which most favor decomposition of organic matter in the soil."
In Africa it has been noticed that dysentery appears with the rainy season, to disappear only at its close; and the same observation has been made of Bengal, while in Lower Egypt the disease follows the inundations of the Nile. Burkhardt says of 10,000 cases that one-half occur in wet hot seasons, two-fifths in dry hot seasons, and but one-tenth in cold seasons. Moreover, the removal of camping-grounds to dry localities has often arrested the disease or checked its further dissemination. Thus, Mursinna states that the removal of the army of Prince Henry of Hesse from Nîmes, where the disease raged fearfully, to Leitmeritz was attended by its immediate cessation, notwithstanding the fact that the soldiers ate large quantities of fruit. A statement of Dillenius, quoted by Heubner, is in this connection exceedingly instructive: "Dillenius had to march with a dysentery hospital of more than 500 patients from July 26 to August 3, 1812, and it required four whole days to accomplish an ordinary nine or ten hours' march. The patients, extremely exhausted, were finally put into a sheep-shed. Here, in the fresh air and lying on hay, they all improved very quickly. By advice of the physician they ate for medicine the fresh whortleberries which they themselves had picked." Werneck attributes the exemption of the city of Halle since the end of the last century to the draining and drying of the neighboring marshes.
On the other hand, numerous observations go to prove that dysentery is likewise prevalent in dry sandy soils where the factors so necessary to the production of malaria are entirely unknown. Thus, Hirsch quotes from Harthill to the effect that dysentery never occurred among the English troops in Afghanistan until they entered upon its thoroughly dry and sandy plains; and from Lidell, who declared that the disease prevailed most in Panama in March, the dry season at this place. Again, a striking confirmation of exemption from dysentery in a marshy region is offered in the Antilles at Grande-Terre, "a wet, marshy plain severely visited by malaria, but used by patients attacked with chronic dysentery at Basse-Terre as the safest place of refuge and recovery."
The rôle of moisture and vegetable decomposition may be, then, summed up in the words of Annesley, that "all situations which furnish exhalations from the decay of animal or vegetable productions under the operation of a moist and hot state of the atmosphere will always occasion dysentery in the predisposed subject—circumstances which, with other causes [italics ours], combine to generate the disease."
Atmospheric vicissitudes, checking of perspiration, catching cold, are synonyms in the present popular as in the ancient professional conception of the genesis of dysentery. "Of the remote causes of dysentery," Johnson says, "I need say little; they are the same in all parts of the world—atmospheric vicissitudes." And in making this statement the author expresses the almost universal testimony of the Indian physicians. "Sudden change of temperature," observes Kaputschinsky of the Trans-Caucasus, where dysentery is rife, "is in this region no rarity. The sultry heat of noon often alternates with a cutting cold wind, and vice versâ. In the same place is now a warm, now a cold, now a glowing hot breeze, and such changes most predispose to dysentery." And McMullin says of the Barbadoes that "it is a curious fact that this disease is most prevalent where from the immediate contiguity of mountains sudden vicissitudes of temperature are experienced." Didelot says also of South France, "It is not the fruits, as people still believe to-day, which act as causes of dysentery, but the sudden variations of the air." Ruthay remarks of the dysentery of China that the most common cause is a chill caught by sleeping in a draught uncovered or in the open air. Metzler attributes the exemption of Stuttgart (since 1811) from any great epidemic to the fact that the city lies in a valley open only to the east, which permits no contrast of hot days and cold nights; and Seeger, in speaking of the epidemic which occurred in Ludwigsberg in 1872 (a city of twelve thousand population, where no epidemic of any kind had appeared since 1834, and where 870 were suddenly attacked with dysentery) that it first broke out in Kaffeeburg in two streets exposed to the wind, and thence spread to different parts of the city. Exposure of the body, especially the abdomen, during sleep or when perspiring, the sudden laying aside of flannel body-clothes, are proceedings, Fayrer says, pregnant with danger in dysenteric regions. A lamentable dysentery appeared, according to Trotter, on board H.M.S. Berwick Oct., 1780, "in consequence of the hurricane on the fifth of the month, by which the clothes and bedding of the seamen, and indeed all parts of the ship, were soaked in water, and many of the men slept for nights together on the wet decks overcome with fatigue and debilitated from want of food." Fayrer also quotes from Moseley the observation that "it often happens that hundreds of men in a camp have been seized with the dysentery almost at the same time after one shower of rain or from lying one night in the wet and cold."