196 K. S. LILLIE. 



cal charge. The sign of the charge is positive in the case of 

 basic, negative in the case of acid bodies, since the former liber- 

 ate negative (OH~) ions, the latter positive (H + ) ions ; the colloid 

 particles themselves are thus left with free positive or negative 

 charges respectively. All particles in a given colloidal solution, 

 having like charges, must for this reason repel one another. 

 Apparently the stability of a colloidal system depends upon this 

 mutual repulsion of the particles of solute, since neutralization 

 of the charge, as by the action of ions of opposite sign, results 

 in an aggregation of the particles and the removal of the colloid 

 from solution ; to this action is to be ascribed the precipitating 

 effect of ions. 



If the particles composing the chromatic filaments and the 

 chromosomes similarly repel one another --as in accordance 

 with their colloid nature they must do --mutual repulsion will 

 play an important part in determining the disposition which these 

 structures adopt within the cell. The chromatin being an acid 

 body must liberate hydrogen ions and become negatively charged, 

 and this to a greater degree the higher its proportion of nucleic 

 acid. I have elsewhere pointed out that sperm-nuclei, which are 

 rich in nucleic acid, show a particularly strong tendency to travel 

 with the negative stream when an electric current is passed 

 through a solution containing them ; this fact may be regarded as 

 confirmatory of the view that the chromosomes, which in com- 

 position are probably very similar to sperm-nuclei, are likewise 

 negatively charged bodies. 1 



Again the prevailingly central position of the nucleus within the 

 cell especially the cell about to undergo mitosis indicates 

 that there exists within the cell an influence tending to draw the 

 nuclear colloids toward a central position. There are reasons for 

 regarding this influence also as electrical in its nature ; it seems 

 highly probable that in the dividing cell the intra-nuclear colloids 

 and the cytoplasmic colloids are opposite in their electrical prop- 

 erties 2 ; they are certainly contrasted in their general chemical 



1 R. S. Lillie, American Journal of Physiology, 8, 1903, p. 273. Also BlOL. BULL. , 

 4, 1903, p. 175. 



2 Proteids are amphoteric bodies, /. e. , may liberate a preponderance either of 

 hydrogen or of hydroxyl ions according to conditions. 



