THE PEOBLEM OF MITOSIS. 
573 
force, and that spindles may be produced otherwise than 
electrically. In a criticism of current theories he allowed 
that the assumption of unlike electric poles seems to be dis- 
proved by tripolar mitotic figures; and showed that, since 
such poles will attract and not repel one another, a further 
assumption is necessary, e.g. that the centrosomes irritate 
the living substance between them, thus causing the growth 
of a spindle that pushes them apart. On the other hand, he 
regarded the smallness of the centi’osomes as a serious objec- 
tion to Biitschli’s explanation of mitosis. 
In 1903 Rhumbler published detailed studies of resemblance 
of mitotic figures and electric lines of force, and again denied 
that the .former can be traced to the latter. He reiterated 
his theory of division, affirming that it not only accords 
with the occurrence of tripolar mitoses, but is the more 
compatible with cytological phenomena. At the same time 
Ziegler adhered to the view that cell division results from a 
change in the protoplasmic outer layer caused by centi’osome 
action. 
In 1905 Hartog said that division is caused by a “ mito- 
kinetic ” force resembling magnetism ; that protoplasmic 
components vary in their respective degrees of permeability 
to this force; and that the most permeable in the cytoplasm 
become converted in mitosis into “material chains” of force, 
differing from geometrical lines of force in that they can cross 
and anastomose. The chromosomes were likewise regarded 
as susceptible to induction, and, since contiguous portions 
presumably carry like charges, cleavage of the spireme and 
subsecpient divergence of daughter - rods in mitosis were 
attributed to mutual repulsion. He believed that cytoplasmic 
traction is the cause of centrosome divergence, and pointed 
out that figures of Kostanecki and Yatsu prove that this 
divergence is not always observed during mitosis. In support 
of his theory he produced several magnetic figures, including 
a triaster obtained with two unlike poles and a third centre 
at zero. He rejected the contraction theory, as held by 
Boveri, firstly, because contractility must be confined to the 
