dren after a stay in the mountains. The anæmia disappeared, while the number of red corpuscles increased. It decreased after return to a lower level, but remained higher than before the sojourn on the mountain. These facts were fully confirmed by the researches of Mercier, von Jaruntowsky and Schroder.
The greater consumption of oxygen induced by the increase in the number of red corpuscles has been measured. According to Schumberg and Zuntz, a man brought to an altitude of 12,467 feet consumes 33 per cent, more oxygen than at sea-level. The increase is not instantaneous. Coindet found that foreigners who had but recently arrived on the Mexican plateau inspired 5.5 liters per minute, while those who had spent a longer period in the same localities took in nearly 6.5 liters.
But while the adaptive changes take place readily and regularly under ordinary conditions in healthy persons, many observations at health resorts of high altitude have shown that in a few cases (old age, certain organic diseases of the heart) they do not take place at all, while in the case of anæmic and neurotic patients they take place only at a moderate altitude and when a cool and bracing atmosphere allows of much outdoor exercise without perspiration. A natural inference to be drawn from those facts is that the climates of all tropical plateaus are not equally conducive to health. While all of them allow life outdoors in any season, and, when not extremely high, are absolutely free from the considerable and sudden changes of temperature which are so injurious to consumptives in the temperate zone, yet the value of such resorts depends mainly on the grade of cooling attending the ascent, especially in the case of general debility, constitutional or even symptomatic. Extremely high altitudes do not agree with the majority of patients; if, at a moderate height (from 3,000 to 5,000 feet), the temperature is low enough to invite exercise, the climate is certainly curative. But if the thermometer reaches daily the eighties, the heart will be unduly quickened during exercise, perspiration will become visible, a tired feeling will appear and the hematose as well as the genesis of blood corpuscles will be interfered with. To suffer from the heat while taking exercise is never invigorating, but, in rarefied air, it is an inconvenience which is the more serious in proportion as the altitude at which it manifests itself is greater. It may be said that, other circumstances being equal, the invigorating value of the climate of a tropical plateau depends on the amount of cold bought at the expense of air rarefaction.
This fact gives the climate of the Central American upland its superiority over that of the broader portion of the plateau which extends from Guatemala to California and which includes the whole Mexican tropical highland. The average yearly temperature of San
