l66 



FINE-STRUCTURE OF PROTOPLASM 



II 



IV 



oT 



when Tj and fg are the two radii ofthe flattened cell indicated in Fig. 105b. 



The unfertilized egg of the 

 st2i-\xtchin, A.rbacia punctnlata, 

 shows a surface tension of 

 0.135 dyne/cm when loaded 

 with two micrograms. Smaller 

 weights give lower values and 

 extrapolation of the tension/ 

 compression curve yields 0.08 

 dyne/cm for the uncompressed egg. As the surface tension is not con- 

 stant but depends on the interior pressure, the surface displays elasticity : 

 this again is evidence of the presence of proteins in the cytoplasm 

 surface, since a layer of pure lipid would not show elasticity. Sols have 

 no elastic properties, so it is evident that the proteins in the surface 

 layer are in a gel-like state. 



Fig. 105. Measurement of surface tension (after 



E. N. Harvey, 1936/37); a) sessile drop, b) 



flattened drop. 



TABLE XXI 



SURFACE TENSION OF PROTOPLASM WITH RESPECT TO SOLUTIONS 

 (according to E. N. HARVEY, 1 93 7) 



Naked protoplasts 



Leucocytes (Lepus caniculus) .... 



„ {Rana pi pi ens) 



Amoeba {Amoeba dnhia) 



Slime mould {Physarum polycephalum) 

 Sea-urchin egg {Arbacia punctulatd) . 

 Salamander egg ij'riturus viridescens) 



Medium 



Ringer sol. + serum 



5? H " 



„ , diluted 



„ , 250 X diluted 



seawater 



pond- water +gum arable 



It is clear that the occurrence of capillary phenomena gives no 

 conclusive evidence of the existence of a true liquid. On the other 

 hand, however, it has not been proved that Hquid cytoplasm possesses 

 an organized structure; it has only been shown that the possibility 

 of such a structure cannot be excluded. 



The same holds good for the results of viscosity studies on liquid 

 cytoplasm, which give valuable information on changes in fluidity. 



