
1904. | The Dual Force of the Dividing Cell. : 551 
III. 
Since the days of Fol many explanations have been put forth, for the most 
part supported by able arguments, and illustrated by ingenious models. 
These explanations may be classified into mechanical, assuming a “pull” or a 
“push,” and kinetic, invoking more subtle “centred forces.” The most able 
advocate of the “ pull theory ” is Boveri. We reject it because, though some 
of the threads attached to the chromosomes retract with them on their 
discession (figs. 2, H, 4)—which would equally occur under the action of 
centred forces—others remain stretched across from pole to pole; nay, in some 
plants the chromosomes merely glide along the threads without any of 
these being retracted. The “push theory” has even less to recommend it, 
despite the able pleas of Meves ; for the spindle-fibres are extremely flexible, 
and show no such changes of form and place as should necessarily accompany 
a pushing action. 
We turn, therefore, to the “ kinetic” theories, of which again are two types. 
(1) Rhumbler and Biitschli have advocated the effects of surface-tension, 
osmosis, and diffusion-currents on the alveolate structure of the cytoplasm, 
regarding the fibres as the extreme effects of radial tensions due to such 
forces on the form and distribution of the alveoli; and Leduc has contributed 
a study of the fields of force produced by diffusion-currents of scarcely more 
than molecular magnitude. We shall see later that the conditions of the 
poles of the spindle are such as to render the action of such forces 
inadmissible to explain the cell-figure, nay, such as to prevent the formation 
of a spindle were the action of these forces propagated to a distance through 
the cytoplasm. 
IV. 
There remains only the supposition that the cell-force is of a “dual” 
character (to use Faraday’s word) like electrostatic force or magnetism ; that 
the cell-centres are the seats of opposite charges; that the fibres of the spindle 
(and of the asters, when such are present) are differentiated in a “ field of force,” 
and transmit lines of force under the action of a pair of “ unlike” poles. 
This conception, present, as we have seen, to Fol at the very birth of modern 
cytology, has been powerfully advocated by many, notably by Guiard* and 
* Giard’s remarks—as early as 1876—are of singular interest, indicating as they do 
the lines on which investigation should be profitably conducted. They occur in a 
résumé of his course at the Faculty of Lille, under the title “ L’Guf et les Débuts de 
Evolution,” communicated to the editor of the ‘ Bulletin Scientifique du Nord’ at his 
request, in order to give his readers some idea of the new discoveries and conceptions in 
the domain of reproduction and cytology. 
He writes: “ L’explication physiologique du phénoméne .. . . doit étre evidemment 
cherchée parmi les phénoménes physico-chimiques et la production de pdles électriques ou 
