;68 



FINE-STRUCTURE OF PROTOPLASM 



II 



„}00 



^ 30 



70 



SO 



/ 



a 



Pressure p in cm H2O 



pressure difference which can be read from a manometer. At the same 

 time he measures the viscosity by following the Brownian movement 

 of particles (dyed by means of chrysoidin) which are embedded in the 

 protoplasm (Pekarek, 1932). In Fig. 106 the viscosity 7] is plotted 

 against the pressure gradient p for plasmic drops from the cells oiCbara 



fragiUs. The viscosity decreases 

 rapidly with increasing pressure 

 (measured in cm HgO), where- 

 as in normal flow of glycerin r\ 

 remains practically independent 

 of the pressure. This experiment 

 shows clearly that protoplasm is 

 not a sol-like liquid, but repre- 

 sents an elastic^' gt\ solution". This 

 does not yet imply a definite struc- 

 ture, although once more this pos- 

 sibility is not ruled out. 



It is otherwise with the devia- 

 tions from Stokes' law. Ac- 

 cording to this law, microscopic- 

 ally visible particles or bubbles in a liquid either fall or rise with 

 constant velocity. Scarth (1927) has ascertained, however, that in 

 cytoplasm the particles do not move with uniform velocity. It looks 

 as though they encounter invisible obstacles, and they fall in a 

 hesitant and jerky manner. According to Scarth, they give the 

 appearance of lead shot which is run through a brush heap. Again 

 and again the falling particles meet with invisible strands, lose speed 

 and change their direction. Accordingly, the cytoplasm cannot be 

 homogeneous but must be full of invisible fibres of a higher density. 

 It does not possess a uniform viscosity, and the results derived 

 from the fall method (Heilbronn, 1914) represent some kind of 

 average value. In Pekarek's viscosity measurements (1930, 1952), 

 which are based on the amplitude of oscillation of particles in Brown- 

 ian movement, the inhomogeneity of the cytoplasm is less apparent, 

 because the oscillatory motion daes not cover a long distance through 

 the cytoplasm and can be studied at a fixed point. 



The values reported for the relative viscosity of the cytoplasm 

 do not prove its true liquid state, even though they are considerably 



Fig. 106. Structural viscosity of the cyto- 

 plasm of Char a fragilis (from Pfeiffer, 

 1936). Abscissa: pressure p in cm HjO. I 

 Cytoplasm at 21° C, II at 12° C; III glyce- 

 rol at 21° C. Ordinate: Viscosity rj in 

 % of the original value. 



