282 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



way, and can only be due to an actual increase of cohesion in the walls of 

 the films or in their contents. In the more solid portions of the protoplasm 

 of Aethalittm, for instance, the reticulum is as thick in relation to the 

 meshes between as in the fluid endoplasm. The altered cohesion might 

 either result from chemical or physical changes in the actual substance of 

 the reticulum, or might be due to modifications of the surface-tension 

 between the walls of the meshes and their contents. In any case, however 

 probable the foam structure may seem, it is not necessarily essential, and 

 the facts collected by Rhumbler 1 fail to afford absolute proof of its 

 universal existence. The properties of colloids may in part be due 

 to their reticulate structure 2 , although surface-tension forces are less 

 prominent than in a froth of soap, bubbles or in an emulsion of two 

 non-miscible substances. 



Active changes in the shape of the walls of the chambers will naturally 

 produce corresponding alterations in the shape of the mass of protoplasm. 

 In addition, the contents of the chambers might be capable of expanding 

 and contracting by imbibing and extruding water. Internal osmotic 

 actions can, however, only come into play when the walls of the chambers 

 are semi-permeable, as are those of small vacuoles. Pulsating vacuoles 

 afford striking instances of rapid expansion and contraction, and when the 

 vacuoles are small the expansion takes place against a strong tendency 

 to contraction due to surface-tension. In the filaments of Cynareae the 

 individual cells are the actively contractile elements, and although the 

 energy of movement is here due to changes of turgor, it might also be 

 produced by changes of tension in the walls of the cells, or of the proto- 

 plasmic meshes. It is indeed not impossible that the mechanism of 

 movement in the stamens of Cynareae may resemble that of cilia, although 

 the latter has still to be determined. 



The power of movement of protoplasm was ascribed to its general power of con- 

 tractility 3 , until Hofmeister 4 attempted to show that it was due to changes of imbibition 

 or swelling. Engelmann 6 also concluded that owing to 'imbibition changes of shape 

 occurred in the molecular aggregations termed inotagmas by him. The importance 

 of the surface-tension of the superficial layer of protoplasm was first put forward by 

 Berthold, while Biitschli showed that the surface-tension actions in an emulsion 

 were even more important. In finely divided emulsions enormous amounts of surface- 

 tension energy may be brought into play, which far more than suffice for the ordinary 

 protoplasmic movements 6 , and may even be able to produce the whole of the energy 



1 Rhumbler, Zeitschr. f. allgem. Physiol., 1903, Bd. II, p. 327. 



1 Cf. Posternak, Ann. de 1'Institnt Pasteur, 1901, T. XV, p. 85; Puuli, Naturw. Rundschan, 

 1902, Bd. xvii, Nr. 25. 



3 Cf. Biitschli, Unters. iiber mikroskopische Schaume, 1892, p. 173. 



* Hofmeister, Flora, 1865, p. 7; Pfknzenzelle, 1867, p. 63. 



s Engelmann, Handbuch d. Physiologic von Hermann, 1879, Bd. I, p. 374. 



* Cf. Ewart. Protoplasmic Streaming in Plants, 1903, pp. 26, 114, 116. 



