Active gas secretion and acclimatisation to altitude

Darwin (1859) used the swimbladder of fishes to show that an organ built for flotation may be converted to respiration.¹ He wrote that physiologists admit it to be homologous with the lungs of higher vertebrates. His passage does not discuss gas pressure. Haldane (1917) supplied that side. He credited Biot with the finding, more than a century earlier, that the gas in the swim bladder of deep sea fishes is nearly pure oxygen.⁶ He noted that oxygen pressure in sea water is only about a fifth of an atmosphere, while inside the bladder it may be 100 atmospheres or more.⁷ He added that Moreau showed in 1877 that fishes secrete just sufficient oxygen into their swim bladders.⁷

Haldane named three factors in acclimatisation to high altitudes: more active lung epithelium in absorbing oxygen, increased breathing, and a higher percentage of haemoglobin.⁴ He gave the first a distinct role. It raises arterial oxygen pressure well above alveolar oxygen pressure, whereas at sea level the two are, as a rule, about equal.⁵ He observed that the purpose of these changes seems clear and that a vitalist would point to it as the interference of a vital principle. He then said the facts must be analysed further.⁵

Bayliss (1915) argued that claims for secretion by the lungs had steadily narrowed. First proposed for the ordinary state, the claim was shown by better methods to follow physical laws. It was then held for muscular exercise, and finally only for acclimatisation to high altitudes.² He asked whether the carbon monoxide method might give different values when haemoglobin is raised, and cited Hasselbalch (1912) on increased hydrogen ion concentration.² In his summary, only the results of Douglas, Haldane and co-workers after some days at altitude resisted explanation by diffusion.³ The two authors thus disagree about whether that residue needs secretion.³⁴

Lung epithelium appears elsewhere in the held texts for other reasons. Wilson (1896) listed it among the tissues of salamanders in which Flemming (1891) found the centrosome and attraction-sphere. Gumuskaya and colleagues (2024) built motile Anthrobots from human lung epithelium. They reported that the structures self-construct in vitro, move by cilia and live 45 to 60 days.⁸ They took the ability of adult somatic human cells to form a novel anatomy with unique behaviours as evidence of plasticity.⁸ These works do not address gas secretion.