lyo 



FINE-STRUCTURE OF PROTOPLASM II 



Speak of a true liquid, for, when static equilibrium is established, the 

 drop is inhomogeneoiis, not only at the surface, but also in bulk. 



To sum up, it can be said that cytoplasm in its Hquid state obeys 

 neither the laws of Newton (Pfeiffer, 1937) nor those of Poiseuille 

 or Stokes (Frey-Wyssling, 1940 a). Although to cytologists it may 

 have the appearance of a liquid, it certainly is no true liquid in the 

 physical sense. We had better not attach too much value to this simi- 

 larity, for we should then be unable to penetrate its submicroscopic 

 fine-structure, since a liquid possesses a structure only in its surface. 

 On the contrary, it is my aim to stress especially the deviations from 

 the physical laws of liquids, as it is precisely these deviations which 

 offer us the chance of elucidating the structural properties of cyto- 

 plasm. 



Gel properties. Often cytoplasm does not flow in Hquid drops, but 

 shows plastic properties. This in itself would not be sufficient to 

 indicate a solid state ; but it is also elastic and to a certain extent pos- 

 sesses a constant shape. The result of plasmolysis is not always separ- 

 ation from the cell wall of a definitely convex drop. On rapid de- 

 hydration with strongly hypertonic solutions the shape in plasmolysis 

 becomes concave or angular, indicating a certain rigidity of the cyto- 

 plasm in this state (Prudhomme van Reine, 1955). 



Especially interesting is the spinning capacity of the cytoplasm, which 

 is apparent from the fact that long strands can be drawn from it 

 (Seifriz and Plowe, 193 i). Often this phenomenon can also be ob- 

 served during plasmolysis in the form of the so-called strands of 

 Hecht (Fig. 107a), although this name is scarcely justified, since their 

 importance was pointed out by Chodat (1907) many years before 

 Hecht (191 2). From Fig. 107 a it is apparent that spherical boundaries 

 as claimed by Rhumbler (1898) occur only in a few fibres in a very 

 imperfect form. A similar fact, which shows the non-liquid state of 

 the cytoplasm, is the "angular plasmolysis" of sea-urchin eggs (Runn- 

 STROM and Monne, 1945 ; Runnstrom, Monne and Wicklund, 1946). 

 In the plasmoptysis of Spirog^ira cells the protoplasm can be drawn 

 out into a long strand which contracts rhythmically (Fig. 107 b). 

 Seifriz (1929) has shown that the cytoplasm of amphibian red cells 

 can be drawn out to three times its normal length and the nucleus 

 even up to 20 times its original length without the occurrence of any 

 drops. All these properties of the cytoplasm are inconsistent with the 



