THE RELATION OF THE VISCOSITY CHANGES OF PROTO- 

 PLASM TO AMEBOID LOCOMOTION AND CELL DIVISION^ 



Warren H. Lewis 

 The Wistar Institute of Anatomy and Biology 

 The viscosity of protoplasm is often readily changeable from sol 

 to gel, gel to sol, and to various intermediate states by unknown 

 internal factors and a few known external ones. The contractile 

 tension which protoplasm exerts varies more or less with its vis- 

 cosity. The contractile tensions exerted by protoplasm play import- 

 ant roles in the activities of cells and organisms, some of which are 

 to be considered in the following pages. 



AMEBOID LOCOMOTION 



The essential aspects of ameboid locomotion have been presented 

 by Mast in his classical account of the structure and locomotion of 

 the ameba. 



Contraction of the posterior part of the superficial gel layer or 

 plasmogel drives the less viscous endoplasm, plasmosol, forward 

 through the body of the cell or organism into the softened or weak- 

 ened anterior end and there produces advancing pseudopods. As 

 the posterior part of the gel layer contracts and shortens, some of it 

 solates or becomes less viscous, mixes with and is carried forward in 

 the endoplasm. At the anterior end, the endoplasm which reaches 

 the lateral walls of the pseudopod gels and gradually extends or 

 builds up the body forward as rapidly as it is torn down at the 

 posterior end. A substratum is needed to move on. This generalized 

 statement applies to the ameba, to the slime mold, to leucocytes, to 

 different types of normal and malignant cells that migrate in tissue 

 cultures, and with certain special modifications probably to all 

 types of organisms and cells which have not developed specialized 

 organs of locomotion such as cilia, flagella, undulatory membranes, 

 and muscles. 



The superficial gel layer is the motor organ in the ameboid type 

 of locomotion. The contractile tension which protoplasm exerts 



' Aided by a grant from the International Cancer Research Foundation. 



[163] 



