with a population less
than 25 to the square mile. Only the small portion contained in India,
southernmost China, and Java shows a density over 125 to the square mile
(or 50 to the square kilometer). This density has to rise to 500 or more
to the square mile before emigration begins. The would-be exiles then
have a wide choice of new homes in other tropical lands, where they find
congenial climate and phases of economic development into which they
will fit. East Indian coolies are found in Cape Colony, Natal, Zanzibar,
Trinidad, and British Guiana, where they constitute 38 per cent. of the
population.

[Sidenote: Effects of tropical climate.]

The redundant population of crowded western and southern Europe also
seek these sparsely inhabited Tropics, but they come heavily handicapped
by the necessity of acclimatization. They leave their homes from
Trondhjem and Stockholm in the north to the Mediterranean in the south,
where the mean annual temperatures vary from 5 deg. to 17 deg. C, (41 deg. to 63 deg.
F.), to seek the Torrid Zone which averages 25 deg. C. or 77 deg. F. over most
of its territory. The effects of a tropical climate are due to intense
heat, to its long duration without the respite conferred by a bracing
winter season, and its combination with the high degree of humidity
prevailing over most of the Torrid Zone. These are conditions
advantageous to plant life, but hardly favorable to human development.
They produce certain derangements in the physiological functions of
heart, liver, kidneys and organs of reproduction. Bodily temperature
rises, while susceptibility to disease and rate of mortality show an
increase ominous for white colonization. The general effect is intense
enervation; this starts a craving for stimulants and induces habits of
alcoholism which are accountable for many bodily ills usually attributed
to direct climatic influences. Transfer to the Tropics tends to relax
the mental and moral fiber, induces indolence, self-indulgences and
various excesses which lower the physical tone.[1435] The social control
of public opinion in the new environment is weak, while temptation, due
to both climatic and social causes, is peculiarly strong. The presence
of an inferior, more or less servile native population, relaxes both
conscience and physical energy just when both need a tonic. The result
is general enervation, deterioration both as economic and political
agents.

[Sidenote: Historical signifi