THE PROTOPLASMIC SYSTEM 



problem of protoplasmic viscosity, with special reference to 

 animal eggs, can be dismissed in a few words. 



The statement made above that the cell contains a high 

 percentage of water, does not imply that the cell-contents 

 flow as freely as water or that they always maintain the 

 same degree of flow. Before the present vogue of measur- 

 ing the viscosity of protoplasm it was shown that the cell- 

 contents have a higher viscosity than water and that this 

 viscosity varies from time to time in a particular cell and 

 differs in different cells. One thinks at once of correlating 

 viscosity with the water-content of a cell: the more water, 

 the less viscosity and vice-versa. To an extent this is true, 

 but the situation is not so simple. Take the case of eggs 

 actively going through the process of division. During 

 each cleavage-cycle, substances move back and forth 

 between nucleus and cytoplasm, between cytoplasm and 

 cytoplasmic inclusions and between egg and external 

 medium. Only in the case of the last named exchange, 

 obviously, does the cell lose water; in the first and second, 

 water moves from place to place within the protoplasmic 

 system. Now since, as the older observations have 

 abundantly shown, changes in viscosity parallel the cell's 

 rhythmical activity in division, it becomes necessary in 

 measuring viscosity-changes to appreciate the fact that 

 water does not shift between nucleus (and structures 

 associated with it) and cytoplasm only; one must also 

 recognize the shift between cytoplasmic inclusions and 

 cytoplasm, especially if one estimates the change in vis- 

 cosity on the basis of the movement of these inclusions, 

 for example, by means of centrifugal force. Since yolk- 

 spheres undergo physical changes during cell-division, one 

 can not in measurements of protoplasmic viscosity assume 

 them as unchanging in deriving conclusions concerning the 

 viscosity of the cytoplasm. Also, in experimentally treated 

 eggs, one can only draw conclusions as to the effect of the 



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