PHYSIOLOGY OF CELL-DIVISION 389 



GENERAL DISCUSSION 



The foregoing experiments afford for the first time clear proof 

 that a reversible change in the properties of the plasma-membrane 

 is associated with the division of the cell-body during mitosis. 

 This change is in the direction of greater instabihty and lower 

 coherence, and apparently of greater permeabihty to diffusing 

 water-soluble substances. According to the membrane-theory 

 of the bioelectric processes, such a change should be accompanied 

 by an electrical variation similar to that of stimulation; evidence 

 that such variations exist is afforded by Miss Hyde's observa- 

 tions on dividing fish eggs.^^ There is, however, need of further 

 observations in this field. 



The close analogy between cell-division and other forms of 

 response^^ — particularly the response of irritable elements to 

 electrical or other stimulation, where a decrease of surface- 

 polarization is undoubtedly the primary or critical event — gives 

 to the above facts a definite bearing on the general theory of 

 stimulation. They support the view that a reversible increase 

 in the permeability of the plasma-membrane is an essential part 

 of the stimulation-process; tliis change apparently determines 

 the change of surface-polarization, and hence the metabolic 

 and other effects within the irritable element. ^"^ According to 

 this view, a reversible surface-change of a kind similar to that 

 associated Tvith cell-division, only relatively rapid, is a normal 

 feature of excitation in irritable cells and elements. 



The relations of such surface-changes to the entire cell-divi- 

 sion process are far from clear in detail. Certain possibilities 

 have already been indicated;" thus it is to be assumed that the 

 plasma-membrane of the resting egg is the seat of an electrical 

 demarcation-potential similar to that of other cells (muscle, 



'M. H. Hyde, Amer. Journ. Physiol., 1904, vol. 12, p. 241. 



*^ I have recently discussed this analogy in a paper in The Journal of Experi- 

 mental Zoology, 1913, vol. 15, p. 23. Cf. also Amer. Journ. Physiol., 1910, vol. 

 26, p. 106. 



'^ For evidence of the connection between changes of permeability and stimu- 

 lation cf. Amer. Journ. Physiol., 1911, vol. 28, p. 197. 



" Page 372 above. 



