RESPIRATION 275 



tory function; its dissociation tension is no longer balanced by an 

 equal or greater partial pressure of oxygen in the air. The ten- 

 sion 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 ' mountain sickness ' so familiar to Alpine 

 climbers (nansea, headache, and marked depression), the undue 

 hyperpnoaa 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 prophylaxis 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 hyper- 

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

 referred to in discussing the normal regulation of respiration (p. 230) 

 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 

 hyperpnosa 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 sick- 

 ness (Haldane). It must be remembered, however, that here the 

 influence of the low barometric pressure is complicated by other con- 

 ditions. For example, while in the pneumatic cabinet, as already 

 stated, diminution of the pressure does not affect the oxygen con- 

 sumption, 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 for- 

 ward that changes in the mechanics as well as in the chemistry of 

 respiration are concerned (the breathing, for instance, taking on a 

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

 [p. 238]), and that there is something not connected with the want 

 of oxygen which diminishes the capacity for muscular work. This 

 ' something ' 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 treat- 

 ment 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. 

 Cutaneous Respiration. It has already been remarked that a frog 

 survives the loss of its lungs for some time, respiration going on 

 through the skin. Indeed, it has been calculated that in the intact 

 frog, under ordinary conditions, as much as three-quarters of the 

 total gaseous exchange may be cutaneous. Two frogs were seen 

 to live thirty-three days, and one even forty days, after excision 

 of the lungs. The effect of exclusion of the pulmonary respiration 

 on the gaseous exchange depends on the previous intensity of the 

 metabolism. If this is high the gaseous exchange sinks markedly ; 

 if it is low there is scarcely any alteration. At their maximum 



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