The humidity caused by an abundant rainfall in any low, hot
country is usually enough to unfit it for human habitation. The
combined effect of heat and moisture upon a fertile soil causes
an excess of both growing and decaying vegetation that fills the
atmosphere with noxious vapors and disease producing germs. The
sultry air is so oppressive that it is more than physical
endurance can bear. The particles of vapor which float in the
atmosphere absorb and hold the heat until it becomes like a
steaming hot blanket that is death to unacclimated life. All of
this is changed where siccity prevails. The rapid evaporation
quickly dispels the vapors and the dry heat desiccates the
disease creating germs and makes them innocuous.

The effect of heat upon the body is measured by the difference in
the actual and sensible temperatures, as recorded by the dry and
wet bulb thermometers. When both stand nearly together as they
are apt to do in a humid atmosphere, the heat becomes
insufferable. In the dry climate of Arizona such a condition
cannot occur. The difference in the two instruments is always
great, often as much as forty degrees. For this reason, a
temperature of 118 degrees F. at Yuma is less oppressive than 98
degrees F. is in New York. A low relative humidity gives comfort
and freedom from sunstroke even when the thermometer registers
the shade temperature in three figures.

A dry, warm climate is a stimulant to the cutaneous function.
The skin is an important excreting organ that is furnished with a
large number of sweat glands which are for the dual purpose of
furnishing moisture for cooling the body by evaporation and the
elimination of worn out and waste material from the organism. As