In 1911 the Anglo-American Pike's Peak Expedition, consisting of Douglas, Haldane, Yandell Henderson, and Schneider,8 spent several weeks on the summit of Pike's Peak with a view to making a thorough study of physiologic adaptation to low atmospheric pressures. The altitude of Pike's Peak is 4290 meters (14,100 feet), which contrasts with the altitude of 4560 meters at which the laboratory on Monte Rosa is located. Pike's Peak, however, differs from Monte Rosa in having a summit which in summer time is almost free from snow, in facility of access by means of a cogwheel railway and in the possession of a very comfortable hotel. The distance from Manitou to the summit is 16.3 kilometers (8.9 miles) by the cog-railway and the difference in altitude between the two localities is 2220 meters (7485 feet). Robinson, the resident manager of the hotel, has resided six months each year for seventeen years on the summit and holds the record for the most rapid ascent of the peak, having accomplished it in two hours and thirty-one minutes. This means walking at the rate of 6.5 kilometers (3.5 miles) per hour and ascending at the rate of 906 meters (2974 feet) during the same interval. Since the body weight was 70 kilograms the hourly heat production might have been (see p. 327):

1 Schumburg and Zuntz: "Pfluger's Archiv," 1896, lxiii, 488. 2 Lee: Fatigue, "The Harvey Lectures," 1905-06, p. 169. 3 Douglas, Haldane, Henderson, and Schneider: "Transactions of the Royal Society," 1912, Series B, cciii, 185.

The requirement of 767 calories per hour exceeds that needed by the trained bicycle rider who rides until exhausted. (See p. 321).

Contrary to the observations of the Zuntz school, the members of the Pike's Peak Expedition found no difference in their metabolism on the summit of Pike's Peak from that at sea-level, either during rest or when taking exercise such as walking at the rate of one to five miles per hour. These results were obtained after acclimatization, and this may account for the difference from those obtained on Monte Rosa.

The ventilation of the lungs of Durig and Zuntz while at rest at different altitudes varied as follows:

The actual amount of inspired air appears to be about the same at different altitudes, an increased volume compensating for increasing rarefaction of the atmosphere.

The atmosphere in which one lives is really the air within the alveoli (Pfluger). Durig and Zuntz have calculated the pressure of oxygen and carbon dioxid within their alveoli at different levels, and, measured in terms of millimeters of mercury, have found them to be as follows:

It is evident from a study of the results that muscular exercise in all these localities produces an increase in the alveolar tension of oxygen and a decrease in that of carbon dioxid. This is brought about by the stimulation of respiration.

It will be interesting to examine the evidence of the effect of decreasing oxygen tension on the capacity of the blood in the lungs to absorb oxygen. The usually accepted doctrine that atmospheric air, shaken with blood, will practically saturate the hemoglobin present, rests upon Hufner's experiments with carefully prepared solutions of hemoglobin. Loewy and Zuntz,1 however, show that if normal blood be used the saturation is 89 per cent, at the most. On the basis of this newer work, Durig and Zuntz2 have calculated the saturation of the hemoglobin within the blood at the different altitudes. At Berlin, oxygen exerting alveolar pressures of 113 and 103 mm. would saturate the blood in the lungs to the extent of 81.9 and 80.5 per cent, respectively. On Monte Rosa alveolar oxygen at pressures of 57 mm. (Zuntz) and 53.2 mm. (Durig) would respectively cause a saturation to the extent of 69.5 and 68 per cent. The lowest recorded oxygen pressure in the alveoli was 48.3 mm. (Durig), which corresponded to 65.9 per cent, of oxyhemoglobin, and was accompanied by severe headache. A quickened heart-beat produced a more rapid circulation than normal. The experimenters find no ground for believing that there was at any time any real oxygen deficiency in any of the important tissues of the body. They consider that their gradual ascent from sea-level prevented the usual disturbances of appetite and digestion which are probably caused by anemia in the abdominal region (mountain sickness).

1 Loewy and Zuntz: "Archiv fur Physiologie," 1904, p. 207. 2 Durig and Zuntz: Loc. cit., p. 442.

Lactic acid has been found in increased amounts in the blood of individuals on high mountains.1 Acidosis quickens the respiration and lowers the carbon dioxid content of the blood and raises the oxygen pressure in the lungs (see p. 218). In mountain sickness the body temperature may rise as high as 420 C.,2 a temperature which favors the free dissociation of oxyhemoglobin.3

1 Galeotti: "Arch. ital. de Biologie," 1904, xli, 80.

2 Caspari and Loewy: "Biochemische Zeitschrift," 1910, xxvii, 405.

3 Barcroft and King: "Journal of Physiology," 1909-10, xxxix, 574.