7 6 IMBIBITION AND MOLECULAR STRUCTURE 



even in the protoplasm itself changes of volume may be observed as the result 

 ' of altered pressure. 



The condensation of water on the surface of the molecules of the substance 

 which it penetrates causes a relatively large amount of energy to be liberated in the 

 form of heat when swelling or non-swelling bodies absorb water. This is, however, 

 a purely physical problem *. 



SECTION 13. Hypotheses of Molecular Structure. 



All ideas of molecular structure rest on a hypothetical basis, and indeed 

 atoms and molecules are simply convenient mental abstractions and may 

 have no actual existence. Just as atoms and molecules are supposed to be 

 the ultimate units of chemical structure, so also are the micellae supposed to 

 be the ultimate elements of which organized bodies are composed, but we 

 cannot postulate for the latter the same degree of certainty and hypothetical 

 importance that we can for the former, so long as it remains uncertain 

 whether the water which penetrates a substance capable of swelling separates 

 molecules, or aggregates of molecules from one another. The power of 

 swelling may be present in bodies of very different molecular structure, and 

 need not necessarily be always precisely similar in character. 



Nevertheless the attempts of Nageli to establish a hypothesis of the 

 intimate structure of organized bodies based upon the phenomena of growth 

 and swelling, and also upon the optical characteristics exhibited by starch- 

 grains, cell-walls, crystalloids, &c., still remain of great value, and more 

 especiallyas his ideas were put forward at a time when physicists and chemists 

 had not as yet paid any attention to the molecular structure of organized 

 bodies. It is true that the mode of growth of starch-grains which Nageli 

 assumed, and on which his first theoretical conclusions were based, has now- 

 been proved erroneous. Nevertheless his clear and precise deductions and 

 conclusions are of all the more value, for in them we have the first conscious 

 attempt to explain the peculiarities of organized bodies by reference to the 

 particular molecular structure to which their several properties are due. 

 The essentials of Nageli's hypothesis are, in a slightly amplified form, still 

 applicable to all the phenomena observed, and even at the present time 

 afford the most thorough and satisfactory explanation of the molecular 

 processes involved in growth and imbibition. 



1 See for example Lehmann, Molecular- Physik, 1888, Bd. I, pp. 289, 548; Ostwald. Lehrb. d. 

 allgem. Chemie, 1891, 2. Aufl., Bd. I, p. 1085 ; Winkelmann, Handb. d. Physik, 1891, Bd. I, p. 480. 

 On the swelling of gelatine, see Wiedemann u. Liideking, Ann. d. Physik, 1885, Bd. XV, p. 53. 

 On production of heat by swelling, starch, &c., Nageli, Theorie d. Canning, 1879, P- I 33 Reinke, 

 Bot. Abhandlung von Hanstein, 1879, Bd. IV, p. 70; Rodewald, Versnchsst., 1894, Bd. XLV, p. 218. 

 On the condensation of the imbibed water, Nageli, Starkekorner, 1858, p. 53 ; Reioke, 1. c., pp. 61 

 and 133. 



