OAT SOME PHYSICAL MANIFESTATIONS OF LIFE 65 



Such exceptions occur in epithelial cells, but it is quite possible, that 

 not the whole cell but only one part of it is in this case the seat of the 

 processes which cause the orientation of the astrospheres or the cen- 

 trosomes. 



R. Lillie has expressed the idea that electrical forces play a role 

 here. - Were this idea correct, it should be an easy matter to control 

 the orientation of the plane of cleavage in the cell by means of a gal- 

 vanic current; such is, however, not the case, at least as far as our 

 present experience goes. If hydrodynamic and "contractile" forces are 

 responsible for the orientation of the astrospheres or centrosomes in the 

 cell, it should be expected that these latter organs are solid or at least 

 more viscous than the rest of the liquids of the cell. If the centro- 

 somes are fixed organs of the cells, and multiply by division, they must 

 naturally be solid or at least possess a solid surface. Alfred Fischer 

 assumed that the formation of astrospheres depended upon a process 

 of coagulation. This has not yet been proved, although this author has 

 imitated the well-known figures of astrospheres in coagulated proteins. 



If the process of nuclear division in transparent cells, e.g. egg cells, 

 is observed, the impression is easily gathered that the astrospheres 

 cause a liquefaction of the nuclear membrane and an emulsification 

 of certain constituents of the nucleus. If this observation be correct, 

 the phenomena of spreading and the phenomena of streaming con- 

 nected with such a process might be the forces which carry the chro- 

 mosomes of the nucleus toward the center of the astrospheres. This 

 assumption is in harmony with the fact that the withdrawal of water 

 from the egg cell diminishes the velocity of the nuclear division,* inas- 

 much as the loss of water may easily increase the viscosity of protoplasm, 

 and thus diminish the velocity of the process of streaming, finally ren- 

 dering it entirely impossible. 



The phenomena of streaming can be demonstrated most beauti- 

 fully in the experiment described above in which eggs of the sea urchin 

 were put into hypertonic sea water, whose concentration was just 

 adequate to prevent the cell division, without preventing the nuclear 

 division. When such eggs are put back into normal sea water after 

 about three hours, the most powerful phenomena of streaming may 

 be witnessed, resulting in the formation of knobs. The streaming 

 seems to occur around the chromosomes or fragments of nuclear mate- 

 rial as a center. Afterwards, each such knob, or projection, formed 

 by the streaming becomes a separate cell.f 



* Loeb, Am. Jour, of Morphology, Vol. 7, p. 253, 1892. 



t This amceboid, character of cell division had been observed and described before by 

 O. and R. Hertwig and called " Knospenfitrchung" 



F 



