Footnotes:
[a]‘The most constant gland in the animal kingdom is the liver.’ Grant's Comp. Anat. p. 576. See also Béclard, Anat. Gén. p. 18, and Burdach, Traité de Physiol. vol. ix. p. 580. Burdach says, ‘Il existe dans presque tout le règne animal;’ and the latest researches have detected the rudiments of a liver even in the Entozoa and Rotifera. Rymer Jones's Animal Kingdom, 1855, p. 183, and Owen's Invertebrata, 1855, p. 104.
[b]Until the analysis made by Demarçay in 1837, hardly any thing was known of the composition of bile; but this accomplished chemist ascertained that its essential constituent is choleate of soda, and that the choleic acid contains nearly sixty-three per cent. of carbon. Compare Thomson's Animal Chemistry, pp. 59, 60, 412, 602, with Simon's Chemistry, vol. ii. pp. 17–21.
[c]‘The size of the liver and the quantity of the bile are not proportionate to the quantity of the food and frequency of eating; but inversely to the size and perfection of the lungs…. The liver is proportionately larger in reptiles, which have lungs with large cells incapable of rapidly decarbonizing the blood.’ Good's Study of Medicine, 1829, vol. i. pp. 32, 33. See Cuvier, Règne Animal, vol. ii. p. 2, on ‘la petitesse des vaisseaux pulmonaires’ of reptiles.
[d]Carus's Comparative Anatomy, vol. ii. p. 230; Grant's Comp. Anat. pp. 385, 596; Rymer Jones's Animal Kingdom, p. 646.
[e]Indeed it has been supposed by M. Gaëde that the ‘vaisseaux biliares’ of some insects were not ‘sécréteurs;’ but this opinion appears to be erroneous. See Latreille, in Cuvier, Règne Animal, vol. iv. pp. 297, 298.
[f]‘La prédominance du foie avant la naissance’ is noticed by Bichat (Anatomie Générale, vol. ii. p. 272), and by many other physiologists; but Dr. Elliotson appears to have been one of the first to understand a fact, the explanation of which we might vainly seek for in the earlier writers. ‘The hypothesis, that one great use of the liver was, like that of the lungs, to remove carbon from the system, with this difference, that the alteration of the capacity of the air caused a reception of caloric into the blood, in the case of the lungs, while the hepatic excretion takes place without introduction of caloric, was, I recollect, a great favourite with me when a student…. The Heidelberg professors have adduced many arguments to the same effect. In the fœtus, for whose temperature the mother's heat must be sufficient, the lungs perform no function; but the liver is of great size, and bile is secreted abundantly, so that the meconium accumulates considerably during the latter months of pregnancy.’ Elliotson's Human Physiology, 1840, p. 102. In Lepelletier's Physiologie Médicale, vol. i. p. 466, vol. ii. pp. 14, 546, 550, all this is sadly confused.
[g] ‘The liver is the first-formed organ in the embryo. It is developed from the alimentary canal, and at about the third week fills the whole abdomen, and is one-half the weight of the entire embryo…. At birth it is of very large size, and occupies the whole upper part of the abdomen…. The liver diminishes rapidly after birth, probably from obliteration of the umbilical vein.’ Wilson's Human Anatomy, 1851, p. 638. Compare Burdach's Physiologie, vol. iv. p. 447, where it is said of the liver in childhood, ‘Cet organe croît avec lenteur, surtout comparativement aux poumons; le rapport de ceux-ci au foie étant à peu près de 1:3 avant la respiration, il était de 1:1.86 après l'établissement de cette dernière fonction.’ See also p. 91, and vol. iii. p. 483; and on the predominance of the liver in fœtal life, see the remarks of Serres (Geoffroy Saint-Hilaire, Anomalies de l'Organisation, vol. ii. p. 11), whose generalization is perhaps a little premature.
These facts, interesting to the philosophic physiologist, are of great moment in reference to the doctrines advocated in this chapter. Inasmuch as the liver and lungs are compensatory in the history of their organization, it is highly probable that they are also compensatory in the functions they perform; and that what is left undone by one will have to be accomplished by the other. The liver, therefore, fulfilling the duty, as chemistry teaches us, of decarbonizing the system by secreting a carbonized fluid, we should expect, even in the absence of any further evidence, that the lungs would be likewise decarbonizing; in other words, we should expect that if, from any cause, we are surcharged with carbon, our lungs must assist in remedying the evil. This brings us, by another road, to the conclusion that highly carbonized food has a tendency to tax the lungs; so that the connexion between a carbonized diet and the respiratory functions, instead of being, as some assert, a crude hypothesis, is an eminently scientific theory, and is corroborated not only by chemistry, but by the general scheme of the animal kingdom, and even by the observation of embryological phenomena. The views of Liebig, and of his followers, are indeed supported by so many analogies, and harmonize so well with other parts of our knowledge, that nothing but a perverse hatred of generalization, or an incapacity for dealing with large speculative truths, can explain the hostility directed against conclusions which have been gradually forcing themselves upon us since Lavoisier, seventy years ago, attempted to explain the respiratory functions by subjecting them to the laws of chemical combination.
In this, and previous notes (see in particular notes 30, 31, 35), I have considered the connexion between food respiration, and animal heat, at a length which will appear tedious to readers uninterested in physiological pursuits; but the investigation has become necessary, on account of the difficulties raised by experimenters, who, not having studied the subject comprehensively, object to certain parts of it. To mention what, from the ability and reputation of the author, is a conspicuous instance of this, Sir Benjamin Brodie has recently published a volume (Physiological Researches, 1851) containing some ingeniously contrived experiments on dogs and rabbits, to prove that heat is generated rather by the nervous system than by the respiratory organs. Without following this eminent surgeon into all its details, I may be permitted to observe, 1st, That, as a mere matter of history, no great physiological truth has ever yet been discovered, nor has any great physiological fallacy been destroyed, by such limited experiments on a single class of animals; and this is partly because in physiology a crucial instance is impracticable, owing to the fact that we deal with resisting and living bodies, and partly because every experiment produces an abnormal condition, and thus lets in fresh causes, the operation of which is incalculable; unless, as often happens in the inorganic world, we can control the whole phenomenon. 2nd, That the other department of the organic world, namely, the vegetable kingdom, has, so far as we are aware, no nervous system, but nevertheless possesses heat; and we moreover know that the heat is a product of oxygen and carbon (see note 32 to chapter ii.). 3d, That the evidence of travellers respecting the different sorts of food, and the different quantities of food, used in hot countries and in cold ones, is explicable by the respiratory and chemical theories of the origin of animal heat, but is inexplicable by the theory of the nervous origin of heat.