ter that confusion and contradiction in the conclusions reached are inevitable. Sanitation, food, water, habits, altitude, character and moisture of the soil, race, traffic, and other controls serve to complicate the problem still further. In most studies of climate and health some, or even many, of these factors have not received attention. Hence the results have usually been incomplete. Local, peculiar, and temporary conditions may play a large part in the prevalence of disease. Overcrowding under unhygienic conditions, especially indoors during cold weather, and traffic by rail, steam, caravan, or on foot, are often more important than climate. The frequent escape of mountain, of desert, and of polar peoples from epidemics is to be attributed in most cases to the smaller chance of importing disease because of little intercourse with the outside world, and of spreading it, when imported, because of the scattered population. It may be noted, however, that the crowding indoors and the sparseness of population in these two cases are more or less directly climatically controlled.

Climate, Micro-organisms and Disease. The cause of disease is now no longer sought directly in meteorological conditions, but in the effects, more or less direct, of these conditions upon the microorganisms which are the specific cause of the disease. Atmospheric conditions may help or may retard the development of the micro-organism, and may strengthen or weaken the individual's power of resistance against the attacks of the germ, as well as

affect his susceptibility. Thus new views have replaced the old. Winds used to be regarded as the chief agents in spreading epidemics: now it is known that disease cannot be carried far by winds, for the micro-organisms do not long maintain their power in the free air and under the sun. Rain has been supposed directly to control the distribution of diseases: now we believe that precipitation acts only indirectly, through drinking water, or through its control of the dust in the air. Dust from dry soil may contain the germs of infectious diseases, and aggravates affections of the respiratory organs. Harmful exhalations are no longer believed to be given off by the soil, but the condition of the soil as to moisture and temperature may affect the development and diffusion of certain micro-organisms. Some parallelism has been discovered between the prevalence of certain diseases, such as diarrhoea and typhoid fever, and soil temperatures or the ground-water level.

Geographical Distribution of Disease. The scheme of classifying disease geographically, on a broad climatic basis, is attractive, but not very satisfactory. For, on the one hand, many diseases are practically universal in extent, showing great independence of climate, and on the other, the history of many diseases is still in the making. In the distribution of disease too many factors are concerned to make any simple and accurate treatment possible as yet. In spite of this complexity, however, certain broad general statements may be made, useful in enabling the

layman properly to co-ordinate his ideas on the subject, and fairly accurate within reasonable limits.

Tropics: General Physiological Effects. The uniformly high temperatures of the tropics, especially when combined with high humidity and the characteristically small diurnal variability of temperature, have certain fairly well established physiological effects. Among these the following are commonly noted: increased respiration; decreased pulse action; profuse perspiration; lessened activity of stomach and intestines, and tendency to digestive disorders; a depression of bodily and mental activity, enervation, indifference, disinclination to exertion,-in fact, a general, ill-defined condition of debility; increased activity of the liver; surexcitation of the kidneys. In damp, hot air, evaporation from lungs is slight; the blood becomes more diluted; there is a deficiency in the number of red corpuscles in consequence of the diminished proportion of oxygen in the air. There is less power to do work; greater fatigue from work; lowered vitality. All this renders the body less able to resist disease. An anæmic condition in the moist tropics is widespread.

Tropical Death-rates. As compared with the death-rates in colder latitudes, tropical death-rates average high. They range from the appalling rate of 483 per 1000 among European troops on the Gold Coast in 1829-1836, through 121 per 1000 for European troops in Jamaica in 1820-1836, down to so low a rate as 14.84 per 1000 for British troops in

India in 1896. These death-rates, however, represent such very diverse conditions of season, climate, race, occupation, soil, mode of life, food, dwelling, etc., that they cannot legitimately be compared with one another. The prevalence of some special disease in exceptionally virulent or widespread development will raise the death-rate of any year far beyond its usual figure. Again, the presence of some insect which causes loss of crops, and the resulting lowered vitality of the people in consequence of insufficient food, may easily swell the death-rate. Nor can these tropical death-rates properly be compared with the death-rates noted under different conditions in other latitudes. (A recent attempt to compare the death-rate among American troops in the Philippines with the general death-rate in certain American cities is an excellent example of the danger of comparing two totally different things). So various and so complex are the controlling factors that critical comparative study is not worth while. Tropical deathrates are certainly high, but this fact should not be attributed solely to the dangers of the climate. Bad sanitary conditions and lack of medical attendance account for many, if not most, of the high tropical death-rates among the natives; and an irrational mode of life explains many deaths among persons coming from cooler climates. Tropical death-rates are being reduced with remarkable rapidity in all countries which are wholly or partly under white control, and especially among European troops in the

tropics. This is the result of experience with tropical conditions, and of the increased precautions which are now taken in selecting and caring for the men.

Hygiene in the Tropics. Under the special conditions of tropical climates, the resident who comes from a cooler latitude needs to take special precautions regarding his mode of life and personal hygiene. A rational, temperate mode of life, especially the avoidance of alcoholic excess; regular exercise; non-fat-producing food; clothing suited to the climate, such as duck or linen for outside garments during the day, and light woollen for the cool of the evening and night; careful attention to the site and construction of dwellings; all possible sanitary precautions; keeping cool during the warmest hours and season by the use of fans or punkahs, by frequent baths, and by abstaining from hard work; protection against mosquitoes by means of screens; frequent change of climate by returning to cooler latitudes,— all these are important. It seems like a contradiction, but it is a fact, that the danger of taking cold in the tropics is very great, and must be carefully guarded against. General Wolseley is reported to have said of the tropics, "not to get cold is to avoid almost certainly all the causes of disease," and a recent writer has well said that these words should be inscribed on the walls of all barracks in the tropics. The situation may be summed up in the rule: "Respect the sun, and rain, and wind; clothe with a view to avoiding chill, and live temperately." The dan