298 RESPIRA TION 



or retain enough oxygen to enable it to perform its respiratory func- 

 tion; its dissociation tension is no longer balanced by an equal or 

 greater partial pressure of oxygen in the air. The tension of carbon 

 dioxide in the blood is also lessened, owing to the dyspnoea and 

 the consequent increase of pulmonary ventilation. 



To such changes, as well as to the cold, some of the deaths in high 

 balloon ascents must be attributed. Messrs. Glaisher and Coxwell 

 supposed that they reached the height of 37,000 feet; the former became 

 unconscious at 29,000 feet (8,800 metres), at which height the amount 

 of oxygen in the arterial blood would probably not exceed 10 volumes 

 per cent., but recovered during the descent. The symptoms of the 

 1 mountain sickness ' so familiar to Alpine climbers (nausea, headache, 

 and marked depression), the undue hyperpncea produced by muscular 

 exertion, and the sleep disturbed by irregular breathing, are also mainly 

 due to deficiency of oxygen in the blood. The most rational prophy- 

 laxis is to leave the high peaks severely alone. But for the enthusiasts 

 who cannot do this a portable apparatus for generating oxygen has been 

 devised. Experiments in the pneumatic cabinet indicate that the 

 hyperpncea is due to the indirect action of want of oxygen already 

 referred to in discussing the normal regulation of respiration (p. 281) 

 that is, to the formation, in consequence of the insufficient oxygen 

 supply, of lactic acid or other substances which have the same influence 

 as carbon dioxide on the respiratory centre so that less carbon dioxide 

 is required to excite the centre. Although the hyperpncea leads to a 

 diminution in the partial pressure of carbon dioxide in the pulmonary 

 alveoli, there is no evidence that lack of carbon dioxide (' acapnia ') is 

 the primary cause of mountain sickness (Haldane). It must be remem- 

 bered, however, that here the influence of the low barometric pressure 

 is complicated by other conditions. For example, while in the pneu- 

 matic cabinet, as already stated, diminution of the pressure does not 

 affect the oxygen consumption, it is relatively much greater on the 

 high mountain levels both during rest and during work than on the 

 plains. This is not the case in balloon ascents. And evidence has been 

 brought forward that changes in the mechanics as well as in the chem- 

 istry of respiration are concerned (the breathing, for instance, taking 

 on a periodic character, with some approach to the Cheyne-Stokes type 

 p. 287), and that there is something not connected with the want of 

 oxygen which diminishes the capacity for muscular work. This ' some- 

 thing ' is perhaps a peculiar excitation of the nervous system in the 

 fierce light of those high levels, which acts not only on the retina, but 

 on the skin, and may even affect the distribution of the blood. It is 

 said that a so-called light bath, as used in the treatment of certain 

 diseases, may increase the quantity of blood in rabbits by 25 per cent, 

 in four hours. The shorter wave-lengths which are relatively more 

 intense in the mountain light are most effective. Recent investigations 

 of the effects of high mountain climates have been conducted by 

 Haldane, Henderson, and others, on Pike's Peak, and by Barcroft and 

 his associates on the Peak of Teneriffe and in the Alps. As already 

 mentioned, Haldane concluded that there was evidence of oxygen 

 secretion by the lungs which became more marked with the duration 

 of residence on the mountain (14,000 feet above sea-level). The total 

 oxygen capacity, and therefore the total amount of haemoglobin, 

 gradually increased. The total volume of the blood was but slightly 

 augmented, and the percentage of haemoglobin rose decidedly. The 

 changes in the circulation have been especially studied by Schneider, 



