e vast forests of the Obi
Valley, they commanded a supply of fish and fur animals which sufficed
for their sparse population. But the greed of the Russian fish dealers
and fur traders, and the devastating work of the lumbermen have made
double war upon Ostyak sources of subsistence.[1434] The appearance of the
white man in Alaskan waters was the signal for the indiscriminate
killing of seal and other marine animals, till the Eskimo's supply of
food and furs has been seriously invaded, from Greenland to the
outermost Aleutian Islands. In all this wide territory, climatic
conditions forbid any substitute for the original products, except the
domesticated reindeer on the tundra of the mainland; but this would
necessitate the transformation of the Eskimo from a hunting to a
pastoral people. This task the government at Washington has undertaken,
but with scant success.

[Sidenote: Cold and health]

In contrast to the numerous indirect effects of a frigid climate, no
direct physiological effect can be positively ascribed to intense cold.
It lays no bodily handicap on health and energy, as does the excessive
heat of the Tropics. The coldest regions where tillage is possible are
tolerable places of residence, because their winters are intensely dry.
That of central Siberia, which is drier than the driest desert, makes
tent life comfortable in the coldest season, provided the tenter be clad
in furs. The low temperatures of the Canadian Northwest for the same
reason have not repelled settlers even from the Southern States.
Negroes, however, meet a climatic barrier in America at the isotherm of
5 deg. Centigrade (41 deg. F.). They are found in New England and Nova Scotia,
generally with a large admixture of white blood; but there and farther
north where the climate is moist as well as cold, they show a fatal
tendency to pulmonary diseases.

[Sidenote: The small amount of tropical emigration]

The acclimatization of tropical people in temperate regions will never
be a question of widespread importance. The negroes were involuntary
immigrants to America, under conditions that can never recur. Their
concentration in the "black belt," where they find the heat and moisture
in which they thrive, and their climatically conditioned exclusion from
the more northern states are matters of local significance. Economic and
social retardation have kept the hot belt relatively underpopulated. The
density map shows much the largest part of it