IV. VISCOSITY MEASUREMENTS 



123 



Hotelling. Probabl}^, their minimal values for protoplasmic viscosity 

 represent approximations to true values. Also their relative values 

 for viscosity at different temperatures are significant. 



Doubtless the best measurements of viscosity by the Brownian 

 movement method are those of Pekarek (23). He follows a procedure 

 used first by Fiirth {24)- Instead of measuring the exact path of 

 movement of a given particle, Pekarek determines the time it takes 



Fig. 3. Path of a particle in Brown- 

 ian movement (after Pekarek, S3). 

 This is diagrammatic, not an actual 

 record. Numbers 1-10 indicate "pas- 

 sages" according to Pekarek's method 

 of counting. 



for a particle to cover a given distance to the right or left of its original 

 position. A microscope ocular with a finely divided series of parallel 

 lines is used. Each time the particle in Brownian movement covers 

 the distance between two sets of lines, this is considered a "passage." 

 Pekarek determines the number of passages for a given time interval. 

 In counting passages, a particle must pass over a complete space be- 

 tween two lines. This is illustrated in Figure 3, which shows the 



