442 THE FORMS OF CELLS [ch. 



complicated arrangement of more or less rigid or elastic structures 



in the wall of the cell, which, like the wire framework in Plateau's 



experiments, restrain and modify the forces acting on the drop. 



In one form of Plateau's experiments, instead of supporting his 



drop on rings or frames of wire, he laid 

 upon its surface one or more elastic 

 coils; and then, on withdrawing oil 

 from the centre of his globule, he saw 

 its uniform shrinkage counteracted by 

 the spiral springs, with the result that 

 the centre of each elastic coil seemed 

 to shoot out into a prominence. Just 

 such spiral coils are figured (after 



"■''• ""-A^rKXcff.' "'""'"■ Koltzoff) in Fig. 148*; and they may 



be regarded as closely akin to those 



local thickenings or striations, spiral ard other, which are common 



in vegetable cells. 



Physically speaking, the protoplasmic colloids are neither simple 

 nor uniform. We begin by thinking of our cell as a drop of a homo- 

 geneous fluid and on this bold simplifying assumption we account 

 for its form to a first, and often to a near, approximation. For the 

 cell is largely composed of fluid "hydrosols," which are still fluid 

 however viscous they may be, and still tend towards rounded, 

 drop-hke configurations. But it has also its "hydrogels," which 

 shew a certain tenacity, a certain elasticity, a certain reluctance to 

 let their particles move on one another; and of these are formed 

 the scarce distinguishable fibrillae within a host of highly specialised 

 cells, the elastic fibres of a tendon, the incipient cell- walls of a plant, 

 the rudiments of many axial and skeletal structures. 



The cases which we have just dealt with lead us to another 

 consideration. In a semi-]:^ermeable membrane, through which 

 water passes freely in and out, the conditions of a liquid surface are 

 greatly modified; in the ideal or ultimate case, there is neither 

 surface nor surface-tension at all. And this would lead us some- 



* As Bethe points out (Zellgestalt, Plateausche Fliissigkeitsfigur und Neuro- 

 fibrille, Armt. Anz. xl, p. 209, 1911), the spiral fibres of which Koltzoff speaks must 

 lie in the surface, and not within the substance, of the cell whose conformation is 

 affected by them. 



