1852, p. 323: but the experiments made by these gentlemen are neither numerous nor diversified enough to establish a general law; still less can we accept their singular assertion, p. 346, that the comparative prices of different foods are a test of the nutriment they comparatively contain.
63
‘Of all the elements of the animal body, nitrogen has the feeblest attraction for oxygen; and, what is still more remarkable, it deprives all combustible elements with which it combines, to a greater or less extent, of the power of combining with oxygen, that is, of undergoing combustion.’ Liebig's Letters on Chemistry, p. 372.
64
The doctrine of what may be called the protecting power of some substances is still imperfectly understood, and until late in the eighteenth century, its existence was hardly suspected. It is now known to be connected with the general theory of poisons. See Turner's Chemistry, vol. i. p. 516. To this we must probably ascribe the fact that several poisons which are fatal when applied to a wounded surface, may be taken into the stomach with impunity. Brodie's Physiological Researches, 1851, pp. 137, 138. It seems more reasonable to refer this to chemical laws than to hold, with Sir Benjamin Brodie, that some poisons ‘destroy life by paralysing the muscles of respiration without immediately affecting the action of the heart.’
65
Prout's well-known division into saccharine, oily, and albuminous, appears to me of much inferior value, though I observe that it is adopted in the last edition of Elliotson's Human Physiology, pp. 65, 160. The division by M. Lepelletier into ‘les alimens solides et les boissons’ is of course purely empirical. Lepelletier, Physiologie Médicale, vol. ii. p. 100, Paris, 1832. In regard to Prout's classification, compare Burdach's Traité de Physiologie, vol. ix. p. 240, with Wagner's Physiology, p. 452.
66
The evidence of an universal connexion in the animal frame between exertion and decay, is now almost complete. In regard to the muscular system, see Carpenter's Human Physiology, pp. 440, 441, 581, edit. 1846: ‘there is strong reason to believe the waste or decomposition of the muscular tissue to be in exact proportion to the degree in which it is exerted.’ This perhaps would be generally anticipated even in the absence of direct proof; but what is more interesting, is that the same principle holds good of the nervous system. The human brain of an adult contains about one and a half per cent of phosphorus; and it has been ascertained, that after the mind has been much exercised, phosphates are excreted, and that in the case of inflammation of the brain their excretion (by the kidneys) is very considerable. See Paget's Lectures on Surgical Pathology, 1853, vol. i. pp. 6, 7, 434; Carpenter's Human Physiology, pp. 192, 193, 222; Simon's Animal Chemistry, vol. ii. p. 426; Henle, Anatomie Générale, vol. ii. p. 172. The reader may also consult respecting the phosphorus of the brain the recent very able work of MM. Robin et Verdeil, Chimie Anatomique, vol. i. p. 215, vol. ii. p. 348, Paris, 1853. According to these writers (vol. iii. p. 445), its existence in the brain was first announced by Hensing, in 1779.
67
Though both objects are equally essential, the former is usually the more pressing; and it has been ascertained by experiment, what we should expect from theory, that when animals are starved to death, there is a progressive decline in the temperature of their bodies; so that the proximate cause of death by starvation is not weakness, but cold. See Williams's Principles of Medicine, p. 36; and on the connexion between the loss of animal heat and the appearance of rigor mortis in the contractile parts of the body, see Vogel's Pathological Anatomy of the Human Body, p. 532. Compare the important and thoughtful work of Burdach, Physiologie comme Science d'Observation, vol. v. pp. 144, 436, vol. ix. p. 231.
68
Until the last twenty or five-and-twenty years, it used to be supposed that this combination took place in the lungs; but more careful experiments have made it probable that the oxygen unites with the carbon in the circulation, and that the blood-corpuscules are the carriers of the oxygen. Compare Liebig's Animal Chemistry, p. 78; Letters on Chemistry, pp. 335, 336; Turner's Chemistry, vol. ii. p. 1319; Müller's Physiology, vol. i. pp. 92, 159. That the combination does not take place in the air-cells is moreover proved by the fact that the lungs are not hotter than other parts of the body. See Müller, vol. i. p. 348; Thomson's Animal Chemistry, p. 633; and Brodie's Physiol. Researches, p. 33. Another argument in favour of the red corpuscules being the carriers of oxygen, is that they are most abundant in those classes of the vertebrata which maintain the highest temperature; while the blood of invertebrata contains very few of them; and it has been doubted if they even exist in the lower articulata and mollusca. See Carpenter's Human Physiol. pp. 109, 532; Grant's Comparative Anatomy, p. 472; Elliotson's Human Physiol. p. 159. In regard to the different dimensions of corpuscules, see Henle, Anatomie Générale, vol. i. pp. 457–467, 494, 495; Blainville, Physiologie Comparée, vol. i. pp. 298, 299, 301–304; Milne Edwards, Zoologie, part i. pp. 54–56; Fourth Report of British Association, pp. 117, 118; Simon's Animal Chemistry, vol. i. pp. 103, 104; and, above all, the important observations of Mr. Gulliver (Carpenter, pp. 105, 106). These additions to our knowledge, besides being connected with the laws of animal heat and of nutrition, will, when generalized, assist speculative minds in raising pathology to a science. In the mean time I may mention the relation between an examination of the corpuscules and the theory of inflammation which Hunter and Broussais were unable to settle: this is, that the proximate cause of inflammation is the obstruction of the vessels by the adhesion of the pale corpuscules. Respecting this striking generalization, which is still on its trial, compare Williams's Principles of Medicine, 1848, pp. 258–265, with Paget's Surgical Pathology, 1853, vol. i. pp. 313–317; Jones and Sieveking's Pathological Anatomy, 1854, pp. 28, 105, 106. The difficulties connected with the scientific study of inflammation are evaded in Vogel's Pathological Anatomy, p. 418; a work which appears to me to have been greatly overrated.
69
On the amount of heat disengaged by the union of carbon and oxygen, see the experiments of Dulong, in Liebig's Animal Chemistry, p. 44; and those of Despretz, in Thomson's Animal Chemistry, p. 634. Just in the same way, we find that the temperature of plants is maintained by the combination of oxygen with carbon: see Balfour's Botany, pp. 231, 232, 322, 323. As to the amount of heat caused generally by chemical combination, there is an essay well worth reading by Dr. Thomas Andrews in Report of British Association for 1849, pp. 63–78. See also Report for 1852, Transac. of Sec. p. 40, and Liebig and Kopp's Reports on the Progress of Chemistry, vol. i. p. 34, vol. iii. p. 16, vol. iv. p. 20; also Pouillet, Elémens de Physique, Paris, 1832, vol. i. part i. p. 411.
70
The law of definite proportions, which, since the brilliant discoveries by Dalton, is the corner-stone of chemical knowledge, is laid down with admirable clearness in Turner's Elements of Chemistry, vol. i. pp. 146–151. Compare Brande's Chemistry, vol. i. pp. 139–144; Cuvier, Progrès des Sciences, vol. ii. p. 255; Somerville's Connexion of the Sciences, pp. 120, 121. But none of these writers have considered the law so philosophically as M. A. Comte, Philosophie Positive, vol. iii. pp. 133–176, one of the best chapters in his very profound, but ill-understood work.
71
‘Ainsi, dans des temps égaux, la quantité d'oxygène consommée par le même animal est d'autant plus grande que la température ambiante est moins élevée.’ Robin et Verdeil, Chimie Anatomique, vol. ii. p. 44. Compare Simon's Lectures on Pathology, 1850, p. 188, for the diminished quantity of respiration in a high
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