THE peoble:m of mitosis. 
583 
in colloid suspensions invariably carry charges of this sign, 
and, even if chromosomes cannot be regarded as such particles, 
the staining reaction of chromatin suggests at least the 
possibility of this potential. In the circumstances G-allardo 
seems to be justified iu saying that this assumption rests upon 
a sound experimental basis ; and, if found to be true, it may 
explain the divergence of daughter-chromosomes in the 
anaphase; for like charges must cause mutual repulsion. We 
will now consider the assumption that the ceutrosomes carry 
positive electric charges. This likewise was suggested by 
the experiments of Lillie, but only in so far as the cytoplasm 
as a whole was said to become inducted. Gallardo, however, 
says, “ Les ceutrosomes sont susceptibles d’acquerir uu poten- 
tiel positif plus eleve que le cytoplasma, qui contient des 
microsomes d’un potentiel plus bas.’^ But I see no proof of 
this : and Gallardo himself realises that it is hypothetical ; for 
he says almost immediately afterwards, “ Le potentiel positif 
du centrosome augmente pour des causes incounues et deter- 
mine sa bipartition et la separation des deux centrosome fils 
eutoures de radiations.” And the second half of this 
sentence clearly shows his object in making the assumption. 
We will, however, suppose that the ceutrosomes represent 
definite positive poles, and will pass on to his interpretation 
of spindle formation. 
By regarding the spindle of the metaphase as being com- 
posed of two half spindles, ejacli formed between a centrosome 
and the chromatin of the equatorial plate, he is able to explain 
all mitotic figures containing chromosomes without asking us 
to imagine spindle formation between like poles. But the 
interpretation fails the moment that we consider chromo- 
someless spindles ; and Gallardo has repeatedly tried to 
remove this objection. Firstly, he proposed charges of 
opposite signs for the ceutrosomes of these spindles; but 
the possibility of this was disproved by Baltzer, who pointed 
out that it is irreconcilable with the formation of triasters in 
which two spindles containing chromosomes are united to 
one that contains none. Gallardo thereupon fell back upon 
VOL. 58 , PART 4 . NEW SERIES. 39 
