130 THE RATE OF GROWTH [ch. 



indistinguishable, whichever of the above salts happen to exist, 

 or to predominate, in their saline habitat. At the same time we 

 still lack (so far as I know) the simple, but crucial experiments 

 which shall tell us whether, in solutions of different chemical 

 composition, it is at equal densities, or at "isotonic" concentrations 

 (that is to say, under conditions where the osmotic pressure, 

 and consequently the rate of diffusion, is identical), that the 

 same structural changes are produced, or corresponding phases 

 of equilibrium attained. 



While Hober and others* have referred all these phenomena to 

 osmosis, Abonyi is inclined to believe that the viscosity, or 

 mechanical resistance, of the fluid also reacts upon the organism ; 

 and other possible modes of operation have been suggested. 

 But we may take it for certain that the phenomenon as a whole 

 is not a simple one; and that it includes besides the passive 

 phenomena of intermolecular diffusion, some other form of activity 

 wliich plays the part of a regulatory mechanismf . 



Growth and catalytic action. 



In ordinary chemical reactions we have to deal (1) with a 

 specific velocity proper to the particular reaction, (2) with varia- 

 tions due to temperature and other physical conditions, (3) according 

 to van't Hoff's " Law of Mass," with variations due to the actual 

 quantities present of the reacting substances, and (4) in certain 

 cases, with variations due to the presence of "catalysing agents." 

 In the simpler reactions, the law of mass involves a steady, gradual 

 slowing-down of the process, according to a logarithmic ratio, as 

 the reaction proceeds and as the initial amount of substance 

 diminishes ; a phenomenon, however, which need not necessarily 



* Cf. Sehmankewitsch, Z. f. w. Zool. xxv, 1875, xxix, 1877, etc. ; transl. in 

 appendix to Packard's Monogr. of N. American Phyllopoda, 1883, pp. 466-514 

 Daday de Dees, Ann. Sci. Nat. (Zool.), (9), xi, 1910; Samter imd Heymons, Abh 

 d. K. pr. Akad. Wiss. 1902; Bateson, Mat. for the Study of Variation, 1894, pp 

 96-101; Anikin, Mitth. Kais. Univ. Tomsk, xiv: Zool. Ce7itralM. vi, pp. 756-760 

 1908; Abonyi, Z.f. w. Z. cxiv, pp. 96-168, 1915 (with copious bibliograpliy), etc 



t According to the empirical canon of physiology, that (as Fredericq expresses 

 it) "L'etre vivant est agence de telle maniere que chaque influence pertui-batrice 

 provoque d'elle-meme la mise en activite de I'appareil compensateur qui doit 

 neutrahser et reparer le dommage." 



