220 PROTOPLASM 



Changes in Viscosity. — Protoplasm passes through a wide 

 range of viscosity values in its normal life. These changes are 

 coincident with changes in physical and physiological activity. 

 When protoplasm is in an active state of streaming, of growing, 

 or of metabolism, its viscosity is relatively low. Resting proto- 

 plasm is of high viscosity. The protoplasm of the growing 

 mother cell of the egg of the seaweed Fucus is of low consistency. 

 As development progresses, the consistency increases until at 

 maturity, when the eggs are in a state of rest awaiting fertiliza- 

 tion, their inner protoplasm is moderately viscous, and the 

 cortical region a soft gel. As the Plasmodium of a slime mold 

 prepares to fruit, its consistency gradually increases until a firm 

 jelly exists throughout. 



It can be stated as a general rule that a state of high metabolic 

 or physical activity means low protoplasmic consistency, and low 

 metabolic or physical activity means high consistency. This 

 statement should not be taken to mean that viscosity determines 

 metabolic rate or any other activity, such as protoplasmic stream- 

 ing, but simply that low viscosity is coincident with an active 

 state. Protoplasmic streaming is certainly facilitated by a 

 decrease in viscosity, and it is usually accompanied by such a 

 change, but the decrease in viscosity is not the cause of the active 

 streaming. 



Changes in protoplasmic consistency occur during cell division. 

 The pioneer worker in this field is Nemec. He found an increase 

 in consistency during the early stages of mitosis. At the com- 

 pletion of division, the viscosity of the protoplasm reverts to 

 the original fluid state. Nemec was able to discern regional 

 differences in consistency at mid-mitosis. Increase in con- 

 sistency is greatest at the periphery of the cell — so great in some 

 cases that the outer cortical zone becomes a firm jelly enclosing 

 an inner, more fluid region. 



Following Nemec, a number of workers studied viscosity 

 changes during the mitosis of echinoderm eggs. Considerable 

 confusion resulted until Fry and Parks carefully repeated the 

 work, using the centrifuge method, and found that during 

 mitosis of Arbacia and other eggs the viscosity is low during the 

 early stages of mitosis, rises during metaphase (mid-mitosis), 

 and reaches its maximum value during anaphase (late mitosis). 

 At cleavage, it drops to the original value. The discrepancy in 



