CYTOPLASMIC GELS 5 



procedures have shown that cytoplasmic gels are res- 

 ponsible for many characteristic activities. The normal 

 condition of these gels is essential for mitosis and cell 

 division, protoplasmic streaming, amoeboid movement, 

 phagocytosis and the maintenance of cell form. For exam- 

 ple the marine protozoon Ephelota coronata throws out 

 fine protoplasmic tentacles, the length of which is many 

 times greater than their diameter. This structure is 

 maintained by the cortical gel layer which lies just inside 

 the plasma membrane in the tentacles. When this gel 

 is liquified by application of high pressure, the operation 

 of surface tension forces immediately breaks the ten- 

 tacles up into a series of fluid droplets. The importance 

 of organised structures is also shown by some experi- 

 ments which were conducted by Moore on the slime 

 moulds. These moulds were able to grow through mem- 

 branes having a pore diameter of the order of i micron. 

 But if they are filtered by pressure through pores as 

 large as loo microns in diameter, the respiration of the 

 mould is decreased by 50%, and if the pore size is not 

 larger than 20 microns, the organism is killed. In consi- 

 dering the significance of these gels in the daily life of 

 the cell, it is important to remember that cell division, 

 protoplasmic streaming, amoeboid movement, phago- 

 cytosis, and the maintenance of cell form can go on 

 quite normally in the absence of the nucleus. In some 

 cases the absence of a nucleus does not exert a pronoun- 

 ced effect for several days after its removal from the cell. 



