[306] Some writers treat physiology as a study of the laws of life. But this, looking at the subject as it now stands, is far too bold a step, and several branches of knowledge will have to be raised from their present empirical state, before the phenomena of life can be scientifically investigated. The more rational mode seems to be, to consider physiology and anatomy as correlative; the first forming the dynamical, and the second forming the statical part of the study of organic structure.
[307] ‘Voulez-vous savoir de quoi dépend le sexe des enfants? Fernel vous répond, sur la foi des anciens, qu'il dépend des qualités de la semence du père et de la mère.’ Renouard, Histoire de la Médecine, Paris, 1846, vol. ii. p. 106; see also, at p. 185, the opinion of Hippocrates, adopted by Galen; and similar views in Lepelletier, Physiologie Médicale, vol. iv. p. 332, and Sprengel, Hist. de la Médecine, vol. i. pp. 252, 10, vol. ii. p. 115, vol. iv. p. 62. For further information as to the opinions which have been held respecting the origin of sexes, see Beausobre, Histoire de Manichée, vol. ii. p. 417; Asiatic Researches, vol. iii. pp. 358, 361; Vishnu Purana, p. 349; Works of Sir William Jones, vol. iii. p. 126; Ritter's History of Ancient Philosophy, vol. iii. p. 191; Denham and Clapperton's Africa, pp. 323, 324; Maintenon, Lettres Inédites, vol. ii. p. 62; and the view of Hohl (Burdach's Physiologie, vol. ii. p. 472), ‘que les femmes chez lesquelles prédomine le système artériel procréent des garçons, au lieu que celles dont le système veineux a la prédominance mettent au monde des filles.’ According to Anaxagoras the question was extremely simple: καὶ ἄρρενα μὲν ἀπὸ τῶν δεξιῶ,θήλεα δὲ ἀπὸ τῶν ἀριστερῶν. Diog. Laert. ii. 9, vol. i. p. 85.
[308] ‘Le metaphysicien se voit comme la source de l'évidence et le confident de la nature: Moi seul, dit-il, je puis généraliser les idées, et découvrir le germe des événements qui se développent journellement dans le monde physique et moral; et c'est par moi seul que l'homme peut être éclairé.’ Helvetius, de l'Esprit, vol. i. p. 86. Compare Herder, Ideen zur Geschichte der Menschheit, vol. ii. p. 105. Thus, too, M. Cousin (Hist. de la Philosophie, II. série, vol. i. p. 131) says, ‘Le fait de la conscience transporté de l'individu dans l'espèce et dans l'histoire, est la clef de tous les développements de l'humanité.’
[309] Considering the very long period during which physiology has been studied, it is remarkable how little the physiologists have contributed towards the great and final object of all science, namely, the power of predicting events. To me it appears that the two principal causes of this are, the backwardness of chemistry, and the still extremely imperfect state of the microscope, which even now is so inaccurate an instrument, that when a high power is employed, little confidence can be placed in it; and the examination, for instance, of the spermatozoa has led to the most contradictory results. In regard to chemistry, MM. Robin and Verdeil, in their recent great work, have ably proved what manifold relations there are between it and the further progress of our knowledge of the animal frame; though I venture to think that these eminent writers have shown occasionally an undue disposition to limit the application of chemical laws to physiological phenomena. See Robin et Verdeil, Chimie Anatomique et Physiologique, Paris, 1853, vol. i. pp. 20, 34, 167, 337, 338, 437, 661, vol. ii. pp. 136, 137, 508, vol. iii. pp. 135, 144, 183, 281, 283, 351, 547. The increasing tendency of chemistry to bring under its control what are often supposed to be purely organic phenomena, is noticed cautiously in Turner's Chemistry, vol. ii. p. 1308, London, 1847; and boldly in Liebig's Letters on Chemistry, 1851, pp. 250, 251. The connexion between chemistry and physiology is touched on rather too hastily in Bouilland, Philosophie Médicale, pp. 160, 257; Broussais, Examen des Doctrines Médicales, vol. iii. p. 166; Brodie's Lectures on Pathology, p. 48; Henle, Traité d'Anatomie, vol. i. pp. 25, 26; Feuchtersleben's Medical Psychology, p. 88; but better in Holland's Medical Notes, 1839, p. 270, a thoughtful and suggestive work. On the necessity of chemistry for increasing our knowledge of embryology, compare Wagner's Physiology, pp. 131, 132 note, with Burdach, Traité de Physiologie, vol. iv. pp. 59, 168.
[310] It used to be supposed that some of the eastern countries formed an exception to this; but more precise observations have contradicted the loose statements of the earlier travellers, and in no part of the world, so far as our knowledge extends, are more girls born than boys; while in every part of the world for which we have statistical returns, there is a slight excess on the side of male births. Compare Marsden's History of Sumatra, p. 234; Raffles' History of Java, vol. i. pp. 81, 82; Sykes on the Statistics of the Deccan, in Reports of British Association, vol. vi. pp. 246, 261, 262; Niebuhr, Description de l'Arabie, p. 63; Humboldt, Nouv. Espagne, vol. i. p. 139; McWilliam, Medical History of Expedition to the Niger, p. 113; Elliotson's Human Physiology, p. 795; Thomson's Hist. of Royal Society, p. 531; Sadler's Law of Population, vol. i. pp. 507, 511, vol. ii. pp. 324, 335; Paris and Fonblanque's Medical Jurisprudence, vol. i. p. 259; Journal of Statist. Soc. vol. iii. pp. 263, 264, vol. xvii. pp. 46, 123; Journal of Geographical Soc. vol. xx. p. 17; Fourth Report of British Association, pp. 687, 689, Report for 1842, pp. 144, 145; Transac. of Sections for 1840, p. 174, for 1847, p. 96, for 1849, p. 87; Dufau, Traité de Statistique, pp. 24, 209, 210; Burdach, Traité de Physiologie, vol. ii. pp. 56, 57, 273, 274, 281, vol. v. p. 373; Hawkins's Medical Statistics, pp. 221, 222.
[311] In Müller's Physiology, vol. ii. p. 1657, a work of great authority, it is said, that ‘the causes which determine the sex of the embryo are unknown, although it appears that the relative age of the parents has some influence over the sex of the offspring.’ That the relative age of the parents does affect the sex of their children, may, from the immense amount of evidence now collected, be considered almost certain; but M. Müller, instead of referring to physiological writers, ought to have mentioned that the statisticians, and not the physiologists, were the first to make this discovery. On this curious question, see Carpenter's Human Physiology, p. 746; Sadler's Law of Population, vol. ii. pp. 333, 336, 342; Journal of Statistical Society, vol. iii. pp. 263, 264. In regard to animals below man, we find from numerous experiments, that among sheep and horses the age of the parents ‘has a very great general influence upon the sex’ of the offspring. Elliotson's Physiology, pp. 708, 709; and see Cuvier, Progrès des Sciences Naturelles, vol. ii. p. 406. As to the relation between the origin of sex and the laws of arrested development, compare Geoffroy Saint-Hilaire, Hist. des Anomalies de l'Organisation, vol. ii. pp. 33, 34, 73, vol. iii. p. 278, with Lindley's Botany, vol. ii. p. 81. In Esquirol, Maladies Mentales, vol. i. p. 302, there is a singular case recorded by Lamotte, which would seem to connect this question with pathological phenomena, though it is uncertain whether the epilepsy was an effect or a cognate symptom.
[312] That the natural powers of the human brain are improving because they are capable of transmission, is a favourite doctrine with the followers of Gall, and is adopted by M. A. Comte (Philosophie Positive, vol. iv. pp. 384, 385); who, whoever, admits that it has never been sufficiently verified: ‘sans que toutefois l'expérience ait encore suffisamment prononcé.’ Dr. Prichard, whose habits of thought were very different, seems, nevertheless, inclined to lean in this direction; for his comparison of skulls led him to the conclusion, that the present inhabitants of Britain, ‘either as the result of many ages of greater intellectual cultivation, or from some other cause, have, as I am persuaded, much more capacious braincases than their forefathers.’ Prichard's Physical History of Mankind, vol. i. p. 305. Even if this were certain, it would not prove that the contents of the crania were altered, though it might create a presumption; and the general question must, I think, remain unsettled until the researches begun by Blumenbach, and recently continued by Morton, are carried out upon a scale far more comprehensive than has hitherto been attempted. Compare Burdach, Traité de Physiologie, vol. ii. p. 253; where, however, the question is not stated with sufficient caution.
[313] None of the laws of hereditary descent connected with the formation of character, have yet been generalized; nor is our knowledge much more advanced respecting the theory of temperaments, which still remains the principal obstacle in the way of the phrenologists. The difficulties attending the study of temperaments, and the obscurity in which this important subject is shrouded, may be estimated by whoever will compare what has been said upon it by the following writers: Müller's Physiology, vol. ii. pp. 1406–1410; Elliotson's Human Physiology, pp. 1059–1062; Blainville, Physiologie Générale et Comparée, vol. i. pp. 168, 264, 265, vol. ii. pp. 43, 130, 214, 328, 329, vol. iii. pp. 54, 74, 118, 148, 149, 284, 285; Williams's Principles of Medicine, pp. 16, 17, 112, 113; Geoffroy Saint-Hilaire, Anomalies de l'Organisation, vol. i. pp. 186, 190; Broussais, Examen des Doctrines Médicales, vol. i. pp. 204, 205, vol. iii. p. 276; Renouard, Hist. de la Médecine, vol. i. p. 326; Sprengel, Hist. de la Médecine, vol. i. p. 380, vol. ii. p. 408, vol. iii. p. 21, vol. v. p. 325, vol. vi. p. 492; Esquirol, Maladies Mentales, vol. i. pp. 39, 226, 429, 594, vol. ii. p. 29; Lepelletier, Physiol. Médicale, vol. i. pp. 139, 281, vol. iii. pp. 372–429, vol. iv. pp. 93, 123, 133, 143, 148, 177; Henle, Anatomie Générale, vol. i. p. 474, vol. ii. pp. 288, 289, 316; Bichat, Anatomie Générale, vol. i. p. 207, vol. ii. p. 444, vol. iii. pp. 310, 507, vol. iv. pp. 281, 399, 400, 504; Bichat sur la Vie, pp. 80, 81, 234, 235; Phillips on Scrofula, p. 9; Feuchtersleben's Medical Psychology, pp. 143–145; Œuvres de Fontenelle, Paris, 1766, vol. v. p. 110; Cullen's Works, Edinb. 1827, vol. i. pp. 214–221; Cabanis, Rapports du Physique et du Moral, pp. 76–83, 229–261, 520–533; Noble on the Brain, pp. 370–376; Combe's North America, vol. i. pp. 126–128. Latterly, attention has been paid to the chemistry of the blood as it varies in the various temperaments; and this seems a more satisfactory method than the old plan of merely describing the obvious symptoms of the temperament. Clark on Animal Physiology, in Fourth Report of the British Association, p. 126; Simon's Animal Chemistry, vol. i. p. 236; Wagner's Physiology, p. 262.
[314] We often hear of hereditary talents, hereditary vices, and hereditary virtues; but whoever will critically examine the evidence will find that we have no proof of their existence. The way in which they are commonly proved is in the highest degree illogical; the usual course being for writers to collect instances of some mental peculiarity found in a parent and in his child, and then to infer that the peculiarity was bequeathed. By this mode of reasoning we might demonstrate any proposition; since in all large fields of inquiry there are a sufficient number of empirical coincidences to make a plausible case in favour of whatever view a man chooses to advocate. But this is not the way in which truth is discovered; and we ought to inquire not only how many instances there are of hereditary talents, &c. but how many instances there are of such qualities not being hereditary. Until something of this sort is attempted, we can know nothing about the matter inductively: while, until physiology and chemistry are much more advanced, we can know nothing about it deductively.
These considerations ought to prevent us from receiving statements (Taylor's Medical Jurisprudence, pp. 644, 678, and many other books) which positively affirm the existence of hereditary madness and hereditary suicide; and the same remark applies to hereditary disease (on which see some admirable observations in Phillips on Scrofula, pp. 101–120, London, 1846); and with still greater force does it apply to hereditary vices and hereditary virtues; inasmuch as ethical phenomena have not been registered as carefully as physiological ones, and therefore our conclusions respecting them are even more precarious.