VISCOSITY 



211 



remember that protoplasm, in addition to being alive, offers 

 all of the problems of the anomalous flow of an elastic liquid. 



Attempts to measure the viscous property of protoplasm with 

 precision are mostly of relatively recent date. A pioneer 

 endeavor to measure a closely related property is that of Pfeffer. 

 He was able, by attaching minute weights to living protoplasmic 

 threads, to determine the load that a strand of myxomycete 

 Plasmodium would support. What was measured was the tensile 



Fig. 106. — A plasmolyzed plant cell with rounded protoplasmic surface (left), 

 and one with concave surface and protoplasmic strands (right). 



strength of protoplasm, or, as Pfeffer expressed it, the cohesive 

 force. 



The Plasmolytic Method. — Under this caption, several 

 methods bearing directly or indirectly on contractility will be 

 considered. 



The configuration of protoplasts (the cell contents as a whole) 

 after plasmolysis is thought to be an indicator of protoplasmic 

 viscosity. The average plant cell when plasmolyzed (in a 

 strong ■ or hypertonic sugar solution) has a smooth, convex 

 surface, with little or no adhesion of the protoplasm to the cellu- 

 lose wall (Fig. 106). This presumably indicates low viscosity. 

 At times, a concave, irregular form, often with many fine attached 

 protoplasmic strands, is obtained; this condition is said to be 

 maintained as a result of high consistency (Fig. 106). But 

 often convex plasmolyzed protoplasts are obtained with many 



