CELLS IN DIVISION 



Chara during this period of mitosis. Protoplasmic streaming within the 

 staminal hair of Tradescantia ceases (Schaede,^^^ Kato^^^) ; Barber^^^ 

 states that 'at metaphase and early anaphase the "boiling" of the 

 protoplasm as seen in the (cinematograph) films of prophase stops 

 completely'. The internal motion of the cell is later resumed. 



It is well known, though as yet inexplicable, that some of these 

 changes resemble the responses of the cell to injury; cell permeability 

 is apparently increased in both instances, though observations of this 

 change in cells during mitosis are largely restricted to marine eggs. 

 That the heightened sensitivity of dividing cells to external agents 

 cannot be due to this cause alone, however, is sufficiently demon- 

 strated by their response to radiation. 



Permeability 



Several methods have been used to demonstrate these variations in 

 permeability of the tgg. The most extended study in this field is that of 

 Herlant,^^' who among many other experiments, followed the 

 permeability of the Paracentrotus egg to water by plasmolysis in hyper- 

 tonic sea water. Lillie^^^ studied the resistance to cytolysis by 

 hypotonic media, while Harvey^^' allowed eggs of Toxopneustes to 

 take up neutral red, and then followed the penetration of sodium 

 hydroxide by the change in colour of the indicator. Most workers have 

 studied the susceptibility to various agents by exposing separate 

 batches of eggs thereto for a short time at different periods after fer- 

 tilization, and have then observed the extent to which the eggs in each 

 batch continued development. In this way were examined the eflfects 

 of ether (Spaulding^^°), cyanide (Mathews^^^), higher alcohols 

 (Baldwin^^^) and ethylene glycol (Stewart and Jagobs^^^). Suscepti- 

 bility and permeability are not necessarily directly related, but their 

 correlation may be admitted from the agreement between results 

 obtained by the different methods. In the eggs of Arbacia, Toxopneustes, 

 and Paracentrotus, soon after fertilization permeability is generally high ; 

 this later decreases and remains low during the early part of the first 

 mitosis. Just before cleavage, the permeability sharply rises, and equally 

 rapidly decreases again when cytoplasmic division is complete. In other 

 eggs, however, these generalizations do not seem to apply. Less clear 

 cut results in Asterias were found by Mathews^^^ and by Stewart and 

 Jacobs; 2 93 Shapiro^^* finds a very slight increase in permeability to 

 water of the egg of Chaetopterus after fertilization, and a marked decrease 

 in that of the frog is described by Krogh et alii^^^ 



I have only been able to find one instance of a research on the per- 

 meability of any other type of cell during mitosis. Stern^^^ studied the 

 penetration of sucrose into isolated pollen mother cells of Trillium. 

 These were placed in a 1-5 molar solution, and became plasmolysed; 



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