[84] Loeb has advocated the view that the “adaptive” growth of working muscles is simply due to the presence of a greater number of molecules in their protoplasm, muscular activity being generated by a process of chemical decomposition.
[85] What has been really proved to exist by the very careful studies carried out by Child, is only certain cases of functional adaptation to mechanical conditions of the strictest kind, and relating to the general mobility only, but nothing more; such adaptations can be said to accompany restitution. See, for instance, Journ. exp. Zool. 3, 1906, where Child has given a summary of his theory.
[86] Even in Vöchting’s experiments (see page [174], note [79]), in which adaptations are mixed with true restitutions in the closest possible manner, a few phenomena of the latter type could most clearly be separated. The stimulus which called them forth must have been one of the hypothetic sort alluded to in a former chapter (see page [113]). The best instances of true restitutions were offered in those cases, where, after the removal of all the bulbs, typical starch-storing cells were formed without the presence of any starch.
[87] Beiträge zur Lehre von den Functionen der Nervencentren des Frosches, Berlin, 1869.
[88] The “secondary adaptations” observed by Vöchting are too complicated and too much mingled with restitutions to allow any definite analysis of the fact of the “secondary adaptation” as such.
[89] General literature: Fröhlich, Das natürliche Zweckmüssigkeitsprincip in seiner Bedeutung für Krankheit und Heilung, 1894. Driesch, Die organischen Regulationen, 1901. A. Tschermak, “Das Anpassungsproblem in der Physiologie der Gegenwart,” in a collection of papers in honour of J. P. Pawlow, St. Petersburg, 1904. Bieganski, “Ueber die Zweckmässigkeit in den pathologischen Erscheinungen,” Annal. d. Naturphil. 5, 1906. Among the general text-books of physiology those by Pfeffer (Pflanzenphysiologie, 1897–1904) and von Bunge (Lehrbuch d. Phys. d. Menschen, 1901) are the fullest on the subject of “regulations.” See also different papers on general pathology by Ribbert.
[90] According to investigations of the last two years, the physics of colloids seems to play as important a part in physiology as osmosis does; we here meet “means” of functioning just as we have already had “means” of organogenesis.
[91] I only mention here that certain modern psychologists have assigned the true law of Weber to the sphere of judgment and not of sensation. If applied to objective reactions only, in their dependence on objective stimuli, it, of course, becomes less ambiguous, and may, in a certain sense, be said to measure “acclimatisation” with regard to the stimulus in question. The mathematical analogy of the law of Weber to the most fundamental law of chemical dynamics seems very important.
As to “acclimatisation” in the more usual meaning of the word, with regard to a change of the general faculty of resisting certain agents of the medium, “immunity” proper is to form a special paragraph of what follows, and to “acclimatisation” towards different degrees of salinity (in algae or fishes) some special remarks will also be devoted on a proper occasion. There remains only “acclimatisation” to different temperatures; but on this topic not much more than the fact is known (see Davenport, Arch. f. Entw. Mech. 2, p. 227). “Acclimatisation” does not allow of a sharp general definition; it may be the result of very different kinds of adaptations in our sense of the word.
[92] I should think that the problem of the re-establishment of irritability, in principle at least, arises even when there is not a trace of so-called “fatigue” or of a “refractory period.” The process of restoring may be so rapid as not to be noticeable, nevertheless some sort of restoring is to be postulated. We may say the “irritability” of an elastic ball is re-established by its elasticity. A certain analogy to this case may perhaps be found in the muscle. But the irritability of nerves with respect to nervous conduction, and of glands with respect to secretion, or of the articulations of Mimosa may be well understood, hypothetically at least, if we assume that the ordinary course of metabolic events is apt in itself to lead to a certain state or condition of the organs in question upon which their irritability is based. Certain general conditions of functioning, as for instance the presence of oxygen for the contraction of the muscle, would better be looked upon as necessary “means” of functioning than as being part of irritability as such. “Fatigue,” of course, may also be due to the absence of such “means” or to abnormal conditions originated by functioning itself.