Note 72 — Chapter II

‘The consumption of oxygen in a given time may be expressed by the number of respirations.’ Liebig's Letters on Chemistry, p. 314; and see Thomson's Animal Chemistry, p. 611. It is also certain that exercise increases the number of respirations; and birds, which are the most active of all animals, consume more oxygen than any others. Milne Edwards, Zoologie, part i. p. 88, part ii. p. 371; Flourens, Travaux de Cuvier, pp. 153, 154, 265, 266. Compare, on the connexion between respiration and the locomotive organs, Beclard, Anatomie Générale, pp. 39, 44; Burdach, Traité de Physiologie, vol. ix. pp. 485, 556–559; Carus's Comparative Anatomy, vol. i. pp. 99, 164, 358, vol. ii. pp. 142, 160; Grant's Comparative Anatomy, pp. 455, 495, 522, 529, 537; Rymer Jones's Animal Kingdom, pp. 369, 440, 692, 714, 720; Owen's Invertebrata, pp. 322, 345, 386, 505. Thus too it has been experimentally ascertained, that in human beings exercise increases the amount of carbonic-acid gas. Mayo's Human Physiology, p. 64; Liebig and Kopp's Reports, vol. iii. p. 359.

If we now put these facts together, their bearing on the propositions in the text will become evident; because, on the whole, there is more exercise taken in cold climates than in hot ones, and there must therefore be an increased respiratory action. For proof that greater exercise is both taken and required, compare Wrangel's Polar Expedition, pp. 79, 102; Richardson's Arctic Expedition, vol. i. p. 385; Simpson's North Coast of America, pp. 49,88, which should be contrasted with the contempt for such amusements in hot countries. Indeed, in polar regions all this is so essential to preserve a normal state, that scurvy can only be kept off in the northern part of the American continent by taking considerable exercise: see Crantz, History of Greenland, vol. i. pp. 46, 62, 338.