THE STRUCTURAL BASIS OF THE BODY 21 



conceived ultramicroscopic particles gemmules which might be discharged 

 from every cell in the body and, passing into the reproductive organs, serve as the 

 material basis of heredity, the first elaborate conception of such a structure was 

 worked out by Nageli (1884). Accorcb'ng to Nageli all organised structures are 

 made Up of micella?, minute particles arranged in definite order and surrounded 

 with water. For growth to take place it was necessary that the system should 

 be in a condition of ' turgor,' which was determined by the amount of water 

 between the micellae. These micellae arose in every case from the division 

 of pre-existing micellae, and the vital properties of the protoplasm were to be 

 regarded as the sum of the changes taking place in the individual micellae. 

 Similar conceptions have been put forward by numerous other observers, 

 each of whom has applied a different name to the elementary living particle, 

 such as 'pangene,' 'plasome,' 'biophor,' ' biogen-molecule,' and many others. 

 The resemblance of these theories to that of Altmann is obvious, though 

 the latter regarded the elementary particle as in many cases of microscopic 

 size and capable of demonstration by appropriate methods of staining. That 

 the cell possesses organs of smaller dimensions than itself, which may give 

 rise to like organs by division, is shown by Schimper's observations on the 

 plastids of plant cells. These apparently are not formed by a process of differen- 

 tiation of the protoplasm, but are continuous from one generation to another 

 and are reproduced by division. There is no doubt, however, that most of the 

 granules to be observed in the cytoplasm are not of this character, but are 

 elaborated by the general cytoplasm out of the foodstuffs which are supplied 

 to it ; and though conceptions such as those of De Vries and Verworn are 

 often of value as a means of describing certain phenomena in the life of the 

 cell and have played a great part in the description of the phenomena of heredity, 

 they cannot be regarded as having any serious justification in fact. At the 

 present time our knowledge of the properties of the colloidal and capillary 

 systems, which must play so great a part in the organisation and reactions of 

 living protoplasm, is much too meagre to justify weight being laid on any theory 

 of the ultramicroscopic structure of protoplasm that can at present be put 

 forward. 



One question which has been much discussed relates to the physical 

 condition of protoplasm. Is it to be regarded as a viscous fluid or as a 

 soft solid ? The perfect potential mobility of the protoplasm of many 

 cells, as instanced by the flow of a substance of an amoeba into its 

 pseudopodia, or the occurrence of rapid streaming movements in the 

 threads of protoplasm found in many plants, e.g. the root hairs of 

 tradescantia, indicates a fluid character for the protoplasm. Against 

 such a character has been urged the fact that in protoplasm we may 

 have shape, organisation, and power of resistance to deformation- 

 qualities which are generally associated with the possession of solidity. 

 It must be remembered, however, that the absence of resistance to 

 deformation, which is characteristic of a liquid, applies only to the 

 internal molecules, and that the surface of any liquid is in a condition 

 of tension which not only limits deformation, but presents considerable 

 resistance to any enlargement of the surface. Small water animals 

 take advantage of this resistance to run freely over the surface of 

 water, although their specific gravity may be greater than that of 



