The Singhalese of hot, humid Ceylon are lighter than the Dravidians to the north. The American Indians cannot be classified in accord with this belief. One of two things then must be true: either the races are not located in the regions to which they are best adapted, or the belief is not well founded. Even so, the darker colored groups may have certain advantages in the tropics, as for instance the Negro with his large sweat glands, and this was the belief of one of our best informed students, the late Dr. Woodruff, who stressed the effects of the actinic rays of the sun.

Consequently we find that man is invariably covered with a pigment which acts as an armor to exclude the more harmful short rays, and moreover the amount of pigment is in direct proportion to the intensity of the light of the country to which his ancestors have proved their adjustment by centuries or millenniums of survival in health and vigor. It is a simple matter of mathematics to show that the intensity of light under the zenith sun in the tropics is the greatest and that the proportion of rays per unit of surface diminishes as we go north in proportion to a function of the latitude. In addition to this the further from the tropics we go the greater is the layer of air which the rays must pass through and the more of them which are absorbed. . . . Undoubtedly the negro, when in the shade, is able to radiate heat better than whites and this enables him to keep cool in the tropics, but puts him at a disadvantage in the north where a white man can keep warmer with less clothing and less fire in the house. But it is a secondary cause enhancing the first, because when it comes to a question of light and cold, nature makes no mistake, but selects a color to exclude the light. Hence in all cold countries, i.e., steppes, plains, and the arctics, there is pigmentation of a color in the lower end of the spectrum, red or yellow, with variations of brown, olive or copper. . . . All these red and yellow colors undoubtedly enable the native to conserve his heat almost as well as the white man, and, at the same time, exclude the dangerous short waves. 1

The ideas of Woodruff had considerable vogue for a time, but the application of his suggestions as to clothing proved

to be of little value. Later observers do not stress the actinic rays. Our information on this point is still inconclusive.

Whites in Tropics

In the best recent summary of the evidence that I have seen, Gregory remains unconvinced as to the validity of the common belief. He claims that there is reason to believe that the whites can stand the heat waves even better than the blacks and states that the English stokers do better than the Lascar on the Red Sea. Kanakas were taken to Queensland to work for three years. Their death rate from 1891-1895 was 42.73, from 1896-1900 it was 30.08, whereas during the same time the death rate of the white population including children and aged was only 12. The Kanakas were excluded by the law of 1901, but the white laborers have stood the climate and the production of sugar has increased. The difficulty with this illustration is that the whites were a selected group which lived under much better conditions than did the Kanakas. Agra is more healthful for the whites than Bombay, which has a lower summer temperature. The crude death rate in Queensland is lower than in the rest of Australia. The planters at Darjeeling at an altitude of 600 feet are reported healthy.

Gregory calls attention to the fact that there are a number of white colonies in the tropics which have prospered. The Dutch colony of Kissav in the Eastern Archipelago, founded at least as early as 1783, and whose climate is called bad, was visited in 1922 by Elkington, who reported "no obvious evidence of physical degeneration." "There is nothing in the available history of these people to show that a tropical climate per se has tended to produce degenerative effects upon them or to limit fertility," yet many of them are blonds. The German colonists in tropical Brazil, Espirito Santo founded in 1847 and now numbering 17,000 or more, and Santa Katherina with some 85,000 inhabitants of the second or third

generation, are said to have better health than the natives. Gregory quotes Arthur Balfour to the effect that the physiological results may be important and that they "are at present the only beacon-lights which may guide us to the haven of certainty." There are many thousands of whites who have lived for generations in Porto Rico likewise. The weakness of these illustrations is that the colonies are in regions carefully selected as suitable to whites, while Porto Rico is a subtropical island very favorably situated.

It is freely admitted by all students that the movement of people to a new country may involve exposure to new diseases and that the resultant death rate is often very high. The Madeira-Mamoré Railroad built in Brazil between 1903 and 1913 is a case in point. Some 400 of 600 German laborers died and the Spaniards, Greek and Barbadians suffered equally. It should not be forgotten that the death rate of all tropical dwellers has been very high without regard to race. Gorgas made Panama healthful but the money cost was enormous. It is admitted also that it may be impossible for any race to maintain standards of work in the tropics to which it has been accustomed elsewhere. In the effort to maintain such standards many have doubtless broken down, and if to disease there has been added recourse to alcoholic stimulants moral as well as physical degeneration is not surprising.

Practically every northerner who goes to the Torrid Zone says that at first that he works as well as at home, and that he finds the climate delightful. He may even be stimulated to unusual exertion. Little by little, however, he slows down. He does not work so hard as before, nor does the spirit of ambition prick him so keenly. On the low, damp seacoast, and still more in the lowland forests, the process of deterioration is relatively rapid, although its duration may vary enormously in different individuals. In the dry interior the process is slower, and on the high plateaus it may take many years. Both in books and in conversation with inhabitants of tropical regions one

finds practical unanimity as to this tropical inertia, and it applies to both body and mind.

The reader will see the relation of this statement to the problem of disease.

An Australian student, Taylor, has written recently in much less hopeful terms of the white man in the tropics. "The chief definite disability resulting from tropical life is found to be tropical neurasthenia, which we learn is associated with depression, irritability, loss of mental activity, and power of concentration." He finds admission to hospitals more numerous than in temperate Australia, from such complaints as dengue, typhoid, alcoholism, etc. "Personally I believe that an adult male, employed in outdoor work, can live as healthily in our tropics as anywhere else. I do not think that this can be said of the women and children, who are even more important in the closer-settlement problem. But it is difficult to get convincing data, as I have stated before, when we come to the somewhat different but vital question of comfort there is no room for argument." Taylor is doubtful about any extensive settlement even of Queensland.

Huntington is likewise skeptical. "Excessive irritability, shortness of temper, is another feature among white residents of the tropics. It cannot be doubted that the discomforts resulting from high temperatures and high humidity are responsible for much of this. One is in a continued bath of sweat day and night, and sleep is difficult and does not refresh one during the wet season at any rate." He found that the death rate of persons born in Queensland was higher than for those born elsewhere in Australia and that women suffered more than the men.®

That which seems clear from the foregoing discussion is not that the white race cannot survive in the tropics in so far as light and heat are concerned but that all men living there

are handicapped by disease and may be unable to exercise the energy necessary to build up a great civilization. Disease may be conquered and then experience will show the importance of the other factors. One-half of the human race lives between the degrees of 20 and 40 north and this it will be noted, excludes Europe, the most densely populated continent. Primitive man may have thriven best in warmer regions but later man has found his greatest opportunities in colder regions. We should not forget that the temperate regions are often hotter in summer than the tropics, for a few days at least.

WORLD POPULATION

A glance at a globe will show that the great land areas of the earth are in the Northern Hemisphere. The total population of the earth must be estimated, as few countries have an accurate census. The following table shows the distribution of population for 1923:

Even if a table such as the one just given could be made wholly accurate, the impression given might be very misleading. Egypt, for instance, has a density of 38 per square mile. But the desert areas of Egypt comprise 335,000 of the 347,000 square miles of the country and have about one