ALPINE ANIMALS 491 



each other, or from polar areas with similar conditions, by wide 

 stretches of lowland with a very different environment contributes 

 greatly to the production of characteristic mountain faunae. 



Low atmospheric pressure. — High mountains are the only places 

 where animal life is subject to reduced atmospheric pressure. It seems 

 to affect only homoiothermal animals, by reason of their high oxygen 

 requirements. For invertebrates, reduced temperature and lack of food, 

 rather than rarefication of the air, limit upward distribution. Beetles 

 reach the last outposts of meadows in the Himalayas, and butter- 

 flies range up to 5640 m. on Mount Everest. Earthworms are found 

 nearly up to the snow line in the Andes. Experiments on vertebrates 

 show varying resistance to reduction of atmospheric pressure. Distinct 

 effects of lack of oxygen are shown by pigeons and men at 350 mm. 

 (of mercury) ; by monkeys at 300 mm.; by cats at 270 mm.; by dogs 

 at 250 mm.; by rabbits at 200 mm.; and by frogs not until 100 mm. is 

 reached. 1 Symptoms of distress (mountain sickness) appear long be- 

 fore these pressures are reached in man and in some other mammals. 

 The greatest altitude reached by mountain climbers without artificial 

 oxygen supply is 28,000 ft. (8540 m.), by the Norton brothers in the 

 Himalayas. With the aid of oxygen apparatus 29,400 ft. (8967 m.) has 

 been attained on Mount Everest. The highest altitude where human 

 settlements persist is at 4860 m. in west Tibet, while herds and herds- 

 men range up to 5500 m. A number of mammals live at higher alti- 

 tudes in Asia, such as wild sheep and ibex, which reach 5800 m., 

 yaks go even higher, wolves 5600 m., and hares to 5500 m. The more 

 delicate races of dogs die in the Andes at 3900 m. within a few days. 

 Vultures and eagles reach an extreme altitude of 7000 m.; this is during 

 flight when the air supply is increased by air resistance. 2 



Numerous observations have been made on the effect on man and 

 other mammals of the reduced pressure at high altitudes. 3 The first 

 effect seems to be a concentration of the blood corpuscles due to the 

 passage of blood serum through the walls of the blood vessels. There 

 seems to be no doubt, however, that this is followed by an actual in- 

 crease in the total number of red corpuscles with increase in the 

 haemoglobin available for combination with larger amounts of oxygen. 

 This appears to be a direct adaptation to the reduced oxygen supply 

 at high altitudes. Peoples of high altitudes are noteworthy for large 

 chest cavities, with increased lung capacity. This was observed by 

 Humboldt in the Andes, and has been shown by exact measurements 

 of the inhabitants of Cerro de Pasco, Peru (4302 m. altitude), who 

 have a chest measurement of 92 cm. compared with 79 cm. in low- 

 landers of equal height. 



