DISPOSITION OF CHROMOSOMES IN MITOSIS. 1 97 



behavior ; at all events they react toward acid and basic staining 

 reagents in precisely opposite manners. This would indicate 

 that the prevalent cytoplasmic colloids are preponderatingly 1 basic 

 in character, i. e., that their particles liberate hydroxyl ions 

 chiefly, and are accordingly for the most part positively charged. 

 It is conceivable that the hydrogen ions from the nuclear proteids 

 and the hydroxyl ions from the cytoplasmic proteids, both of 

 which ions have high migration velocities, find their way through- 

 out the entire cell and unite with each other to form water. The 

 colloids themselves, on the other hand, though of opposite sign, 

 are unable so to unite, or can unite only partially, on account of 

 the impossibility of their diffusing through one another ; they 

 are therefore left in the cell with free and opposite charges. Pos- 

 sibly a partial union of the nuclear and the cytoplasmic colloids 

 may take place at the boundary between the two aggregates ; it 

 is known that colloids of opposite electrical sign will precipitate 

 each other when their solutions are mixed, presumably by each 

 effecting a neutralization of the other's charge. 2 Now it is a 

 very remarkable fact that the nucleo-proteids of the cell are 

 almost invariably separated from the cytoplasmic proteids by a 

 well defined membrane, the " nuclear membrane," which is very 

 possibly a precipitation-membrane formed at the surface of con- 

 tact between the two oppositely charged colloidal aggregates. If 

 this is so, it becomes intelligible why further neutralization of the 

 charges is prevented and how each set of colloids is enabled to 

 retain its charge in the presence of the other. The condition 

 thus reached is that of a negatively charged aggregate, viz : the 

 nucleus with its contained chromatin, in the midst of a posi- 

 tively charged field consisting of the numerous positively charged 

 colloidal particles of the cytoplasm. 3 



The central position of the chromatin is now easily explained 

 as due to the attraction which the aggregate of oppositely charged 

 cytoplasmic colloids exercise upon it, the resultant effect of all 



f. R. S. Lillie, loc. dt. 



2 Biltz, Berichte.der deutschen chemischen Gesellschaft^ 37, 1904, p. 1095. 



3 This suggests J. J. Thomson's conception of the atom as a system of negative 

 electrons moving in a field of uniform positive electrification. It would be strange if 

 such a parallel should exist between the respective units of living and of lifeless 

 matter. 



