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49 See also (int. al.), John Bernoulli, de Motu Musculorum, Basil., 1694; Chabry, Mûˋcanisme du Saut, J. de lãAnat. et de la Physiol. XIX, 1883; Sur la longueur des membres des animaux sauteurs, ibid. XXI, p. 356, 1885; Le Hello, De lãaction des organes locomoteurs, etc., ibid. XXIX, p. 65ã93, 1893, etc.

50 Recherches sur la force absolue des muscles des Invertûˋbrûˋs, Bull. Acad. E. de Belgique (3), VI, VII, 1883ã84; see also ibid. (2), XX, 1865, XXII, 1866; Ann. Mag. N. H. XVII, p. 139, 1866, XIX, p. 95, 1867. The subject was also well treated by Straus-Dû¥rckheim, in his Considûˋrations gûˋnûˋrales sur lãanatomie comparûˋe des animaux articulûˋs, 1828.

51 The fact that the limb tends to swing in pendulum-time was first observed by the brothers Weber (Mechanik der menschl. Gehwerkzeuge, GûÑttingen, 1836). Some later writers have criticised the statement (e.g. Fischer, Die Kinematik des Beinschwingens etc., Abh. math. phys. Kl. k. SûÊchs. Ges. XXVãXXVIII, 1899ã1903), but for all that, with proper qualifications, it remains substantially true.

52 Quoted in Mr John Bishopãs interesting article in Toddãs Cyclopaedia, III, p. 443.

53 There is probably also another factor involved here: for in bending, and therefore shortening, the leg we bring its centre of gravity nearer to the pivot, that is to say, to the joint, and so the muscle tends to move it the more quickly.

54 Proc. Psychical Soc. XII, pp. 338ã355, 1897.

55 For various calculations of the increase of surface due to histological and anatomical subdivision, see E. Babak, Ueber die OberôÙflûÊchenentôÙwickeôÙlung bei Organismen, Biol. Centralbl. XXX, pp. 225ã239, 257ã267, 1910. In connection with the physical theory of surface-energy, Wolfgang Ostwald has introduced the conception of specific surface, that is to say the ratio of surface to volume, or Sã₤ãã₤V. In a cube, V =ã₤lÿ£¢³ã₤, and S =ã₤6lÿ£¢²ã₤; therefore Sã₤ãã₤V =ã₤6ã₤ãã₤l. Therefore if the side l measure 6 cm., the ratio Sã₤ãã₤V =ã₤1, and such a cube may be taken as our standard, or unit of specific surface. A human blood-corpuscle has, accordingly, a specific surface of somewhere about 14,000 or 15,000. It is found in physical chemistry that surface energy becomes an important factor when the specific surface reaches a value of 10,000 or thereby.

56 Though the entire egg is not increasing in mass, this is not to say that its living protoplasm is not increasing all the while at the expense of the reserve material.

57 Cf. Tait, Proc. R.S.E. V, 1866, and VI, 1868.

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