ENERGETICS OF KARYOKINESIS 383 



mentioned above. On the " outer " side of the centrosomes 

 can be seen starlike radiations (astral rays) recognisable as indi- 

 cations of incomplete lines of force which run externally to those 

 stronger interpolar lines which constitute the spindle. 



The nucleus is composed of material of fairly high " permea- 

 bility " and, therefore, may be expected to travel towards the 

 equatorial axis. This is found to be so. In some cases the 

 nucleus is wholly, and in other instances it is only partially drawn 

 into the field between the centrosomes. Differences, too, exist 

 in the relative development of asters and spindle which are 

 capable of explanation by analogy to the magnetic model. If, 

 in the experiment with iron filings, the field were surrounded by an 

 iron ring, the majority of the lines of force would pass round by 

 the ring. That is, the interpolar lines would be slight and the 

 extra-polar rays would be heavy. Similarly, we may correlate 

 a mitotic figure having good astral rays and a poor spindle with a 

 marked " permeability " of the surface of the cell. 



One would be entering the realms of pure hypothesis if physico- 

 chemical interpretations were attempted of the various stages of 

 karyokinesis. The constitution of protoplasm vaguely stated 

 as an emulsion of various lipoids in a complex protein-water 

 emulsoid with various crystalloids in solution or adsorbed, presents 

 excellent opportunities for the theorist to draw parallels between 

 certain manifestations of force in living things and in dead matter. 

 The mechanisms underlying these processes are as yet unknown. 

 The processes themselves, like all Other changes in matter, are 

 accompanied by changes in electrical potential. These changes 

 are measurable and are not constant but fluctuate (even reversing 

 in direction) at epochs coinciding with phases of development. 



We are now in a position to consider the actual cause of cell 

 division. To state why the cell must divide to argue from a 

 surface- volume ratio is to presuppose a cell consciousness or to 

 postulate an external directing force both alternatives being 

 without the domain of physics. The use of the final cause or the 

 argument that division is of obvious advantage to the cell, sheds 

 no light on the mechanism involved. Consideration must be 

 given to the forces at work in the cell. Further, experiments 

 such as the much quoted one of Brailsford Robertson, where an 

 oil drop is divided by the imposition on it of a thread soaked in 

 alkali, are not very illuminating. The energy of cell division is 

 not external to the cell but depends entirely on a redistribution 

 of forces inside the cell. 



