Differential Diagnosis.—The diseases and morbid conditions which are most likely to be mistaken for cholera morbus, both in children and adults, are epidemic cholera, and the effects of direct irri tants, such as toxic doses of arsenic, poisonous mushrooms, overripe fruits, and the ptomaines occasionally in ice cream, cheese, and canned meats, and gastro-enteric inflammation. The clinical phenomena presented by severe cases of cholera morbus and of cholera Asiatica are so nearly identical that a reliable diagnosis cannot be founded on these phenomena alone. It is true that a very large proportion of the cases of epidemic cholera commence with painless, watery diarrhceal discharges continuing from one to three or more days, before the violent paroxysms of vomiting, purging, and cramps begin. When cholera mor bus commences with diarrhcea the dis charges are accompanied by more ordi nary griping or abdominal pains and the early passages are more mixed with the ingesta and appearances of bile. In doubtful eases the discovery of the cholera bacillus of Koch in the intes tinal discharges is claimed to be the only reliable proof that the case is one of true epidemic cholera. But there is so close a resemblance between the com mon bacillus of Koch and that found by Prior and Finkler in the discharges of ordinary cholera morbus as seen under the microscope, that cultures are re quired to complete the distinction be tween them. Cases of sudden and severe vomiting and purging caused by irri tating ingesta are more readily distin guished from cholera morbus by their commencing very soon after the taking of bad food or poisonous substances, and by the existence of more constant burning sensations or distress at the epigastrium. The discharges also early show intermixture of mucus and some times streaks of blood, which, in cholera morbus, seldom appear until in the ad vanced stage of the disease. In gastro enteritis the gastric and intestinal dis charges are, from the beginning, less copious and are mixed with mucus; there is more epigastrie distress, more febrile heat, and more frequent efforts to vomit, with the ejection of only small quantities of mucus of a green or yellow color.
In the advanced stage of some of the more severe cases of cholera morbus a condition of morbid vigilance, with roll ing of the head, tossing of the hands, and moaning, supervened and sometimes ended in a general convulsion. These symptoms have generally caused the friends, and sometimes the attending physician, to think that disease was de veloping in the brain. I have seen a few of such cases treated with cold applications to the head and blisters be hind the ears, while the real cause of the symptoms was cerebral anmmia or exhaustion.
Microscopical examinations have shown the presence of a variety of micro-organisms in the discharges of cholera morbus, but no one of them has yet proved to be of diagnostic value.
Etiology.—Abundant clinical observa tions and vital statistics have shown that cholera rnorbus, both in children and in adults, prevails most in those parts of the temperate zone characterized by a wide range of temperature between the coldest days of winter and the hottest days of summer. Its prevalence is lim ited almost wholly to the months of June, July, August, and September, gen erally commencing with the first pros trated wave of high temperature during the last week in June or the first in July and reaching its greatest prevalence by the middle of the latter month. Thus, of the 1119 deaths from cholera morbus and cholera infantum in Chicago in 1896, 1 was reported in January, 2 in April, 2 in May, 180 in June, 485 in July, 339 in August, 108 in September, 1 in October, and 1 in December. In 1895 the whole number of deaths from the same disease was 1345, of which 6 were reported in March, 3 in May, 187 in June, 554 in July, 315 in August, 275 in September, 2 in October, 2 in November, and 1 in December. So great
a mortality occurring regularly during the hottest months of each year induced me to make the subject a special study during the decade following 1870. The facts gathered by such study justified the conclusion that cholera morbus, in both adults and children, commences uni formly- during the first period of high summer temperature continuing day and night not less than five days con secutively, and new cases appear during each similar hot period for sixty of ninety days. It is not simply high tem perature for a single day, or for three or four days while the nights remain cool, but high temperature both day- and night, four or five days in succession, that favors the development of the dis ease. If the air is stagnant from absence of wind, or overcrowding and narrow streets, as in populous cities, the number of attacks will be much increa_sed. On the other hand, cities and towns so located that the nights are favored by cooler breezes from the sea suffer but little from ordinary choleraic attacks.
Nearly all the writers on general prac tice and on diseases of children mention high temperature and overcrowded and poorly ventilated dwellings as merely predisposing causes of the disease under consideration; while they enumerate, as direct exciting causes, the taking of im proper food, as mixed salads, impure or changed milk, impure and confined air, and, in infants, the progress of denti tion and the nursing of overworked, improperly fed, and unhealthy mothers Or nurses.
That all these causes exist and occa sionally directly excite attacks of cholera morbus in both children and adults there can be no doubt. _But as they all exist in all large cities and populous districts, and at all seasons of the year, if they were the chief causes of the disease it should prevail at all seasons of the year instead of being confined to three or four of the hottest months, and it should pre vail as much in cities so located as to receive cool breezes during the sununer nights as in those that do not. There is probably as much lack of ventilation and as much use of poor or adulterated milk and other articles of food during the winter as during the summer. And therc are quite as many overworked and badly-fed mothers, and as many infants "cutting teeth," in the month of Janu ary as in July, yet, as stated above, dur ing the years 1895 and 1896 in Chicago only 1 death was reported from cholera morbus and infantum in January and 1039 in July. Such results show un mistakably that high temperature, con tinued through several consecutive days and nights, constitutes the ruling factor in the causation of the disease under consideration. The higher the tempera ture of the atmosphere, the less amount of oxygen is contained in each cubic foot, and consequently less reaches the air cells of the lungs at each breath and less is distributed to the tissues of the body in a given time. Hence the nerv ous and muscular structures become re laxed, the watery elements of the blood ' escape, the perspiration carrying with it the free salts of the blood, which still further diminishes its capacity for taking up oxygen from the of the lungs. If this condition of things is continued through several successive days and nights, the capillaries of the mucous membranes of the stomach and intes tines relax, and allow the serous element of the blood to escape more freely than perspiration from the cutaneous sur faces, and choleraic discharges more or less profuse are the result. If the patient is confined in a close, ill-ven tilated room, as is likely to he the case with young children, especially at night, the evil effects are mnch increased. And close investig-ation shows that the begin ning of a large majority of the cases occurs during the last half of the night or early in the morning.