THE PROBLEM OP MITOSIS. 
585 
acliromatic figure can now be no index of the actions at the 
poles. He says, “Les deux nouveaux noyaux en formation 
attirent le cytoplasma positif et determinent ainsi la seg- 
mentation cellulaire. Le contour exterieur do la cellule suit 
dans cette segmentation le forme des equipotentielles succes- 
sives entre deux centres homonymes. L’approximation des 
deux nouveaux noyaux en formation aux centrosomes re- 
spectifs, de charge de nom contraire, produit une coagulation 
entre colloides de signes opposes (formation de nouvelles 
membranes nucleaires) et une neutralisation qui determine 
une periode d’equilibre.’’ From this it is evident that the 
interpretation depends upon electric effects between the 
negatively charged chromatin and the positively charged 
centrosomes, and that the spindle itself is not actively con- 
cerned in these processes. But, although the assumption of 
a negative electric charge for the chromosomes has been 
shown to rest upon an experimental basis, the assumption 
that the centrosomes have a positive potential higher than 
that of other microsomes is hypothetical ; and upon the latter 
assumption as well as upon the former rests his interpretation 
of both spindle formation aud cell division. His proposition 
relating to bipolarity in the mitotic process is therefore 
entirely speculative so far as the centrosomes are concerned ; 
and we must remember that, even if these are eventually 
found to be definite positive poles, electricity may not be the 
primaiw factor in division, and, in any case, the theory will 
require modification before it can explain the mitosis of those 
plants in which centrosomes do not exist. 
We will now consider Rhumbler’s theory. As already 
stated, the centrosome is said to arise as a local solidification 
of the alveolar wall substance ; the solidification involves 
increased adhesion at this spot, and fluid is accordingly 
driven towai’ds portions of the cell where pressure is less. 
The consequent loss of fluid in the reticular rays causes them 
to shorten, and thus exercise a tractive force that results in 
division. That the theory has been carefully thought out is 
evident ; for it postulates a concatenation of events in mitosis. 
