pressure, and (ix.) the prevailing winds. Generally
speaking, the relative purity of the air--i.e. absence of septic solid
particles--is an important consideration; while cold acts as a stimulant
and tonic, increasing the amount of carbon dioxide exhaled in the
twenty-four hours. Different individuals, however, react both to heat
and cold very differently. At health resorts, where the temperature may
vary between 55 deg. and 70 deg. F., strong individuals gradually lose
strength and begin to suffer from various degrees of lassitude; whereas
a delicate person under the same conditions gains vigour both of mind
and body, puts on weight, and is less liable to disease. And a
corresponding intensity of cold acts in the reverse manner in each case.
Thus a health resort with a moderate degree of heat is very valuable for
delicate or elderly people, and those who are temporarily weakened by
illness. Cold, however, when combined with wind and damp must be
specially avoided by the aged, the delicate, and those prone to gouty
and rheumatic affections. The moisture of the atmosphere controls the
distribution of warmth on the earth, and is closely bound up with the
prevailing winds, temperature, light and pressure. In dry air the
evaporation from both skin and lungs is increased, especially if the
sunshine be plentiful and the altitude high. In warm moist air strength
is lost and there is a distinct tendency to intestinal troubles. In
moist cold air perspiration is checked, and rheumatic and joint
affections are very common. The main differences between mountain air
and that of the plains depend on the former being more rarefied, colder,
of a lower absolute humidity, and offering less resistance to the sun's
rays. As the altitude is raised, circulation and respiration are
quickened, probably as an effort on the part of the organism to
compensate for the diminished supply of oxygen, and somewhat more
gradually the number of red blood corpuscles increases, this increase
persisting for a considerable time after a return to lower ground. In
addition to these changes there is a distinct tendency to diminished
proteid metabolism, resulting in an increase of weight owing to the
storage of proteid in the tissues. Thus children and young people whose
development is not yet complete are especially likely to benefit by the
impetus given to growth and the blood-forming organs, and the
therapeutic value in their case rarely fails. For older people