THE PEOBLEM OP MITOSIS. 
579 
tension and consequent constriction of the cell. This, how- 
ever, has been denied by McClendon, who pointed out that no 
appreciable synthesis of nuclein occurs during cleaviige, and 
that Masing and Shackell have found as much nuclein in the 
two-cell stage of the egg as in the blastula. Moreover, he 
described an experiment showing that the surface tension is 
not diminished, but relatively increased. 
The electric interpretation of mitosis was advocated last 
year by Pentimalli, who, with Gallardo, assumes a negative 
charge for the chromatin. In his experiments, which 
resemble those of Lillie, he showed that the chromosomes 
move towards the positive pole when an electric current is 
passed through the cell; and, Avhen the cell membrane is 
perforated, free themselves from spindle and cytoplasm and 
pass into neighbouring cells. He affirmed that the spindle is 
not similarly affected, but seems to be drawn by the chromo- 
some movement ; and suggested that the electric charge of 
the chromatin increases as mitosis proceeds. His results 
have since been corroborated by McClendon. 
Gallardo has recently published a paper summarising his 
views and offering a further explanation concerning chromo- 
someless spindles. He again points out that the theory of 
unlike poles cannot account for either the divergence of 
centrosomes in the prophase or that of daughter chromosomes 
in the anaphase ; that it is impossible on this assumption to 
produce tetrasters with two diagonal spindles, oi- to produce 
triasters without having' recourse to a neutral centre ; and 
that the staining reactions at the Gvo poles appear to be 
inconsistent with the theory. He affirms that these difficulties 
are removed by assuming the poles to be of the same sign, 
and says that all chromosomeless spindles are formed by the 
stretching of the viscous and elastic cytoplasmic medium. 
Disquisition. 
Consideratiou of the various theories outlined on the pre- 
ceding pages and of the objections that have been raised 
against them shows that no unanimity of opinion exists 
