178 FINE-STRUCTURE OF PROTOPLASM IE 



be imitated by artificial drying at room temperature, since the change- 

 in the framework structure has to proceed step by step along with, 

 the dehydration caused by the neutralization or screening of the 

 hydrophilic groups, without changing those configurations of the 

 molecular structure which are necessary for the maintenance of life^ 

 But by the modern procedure oi free^e-drying a method has been found 

 which permits evaporation of the hydration water without altering am~ 

 structure essential to life. Freeze-dried bacteria can be preserved in- 

 definitely ; and this method seems to be very promising for the preven- 

 tion of denaturation when fixing submicroscopic protein structures^ 



The physical properties fluidity^ plasticity and elasticity must be at- 

 tributed to the character of the junctions between submicroscopic 

 particles. The more these are dissolved, the more liquid the cytoplasm, 

 becomes. However, the junctions must never all be weakened at the 

 same time. Jn other words, the cytoplasm must never become a true 

 sol in which all particles can move freely. Certain bonds are always 

 preserved and these cause the elastic properties. The dissolution of" 

 all junctions would result in the death of the cytoplasm by liquefaction^ 



The great marvel of the Uving framework is its striking mobility,, 

 which becomes apparent in protoplasmic flow. In this flow the chains, 

 are orientated not only in small submicroscopic, but even in micro- 

 scopic regions, as indicated by the visible strand formation. The paral- 

 lel alignment of the chains is often so pronounced that birefringence 

 of flow occurs (Ullrich, 1936a; amoeboid movement of the rhizo- 

 podiae, Schmidt 1937a, 1941b). The whole movement is only intel- 

 ligible if a great number of junctions are continuously being formed^, 

 only to be broken down shortly afterwards. The jimdamental dijference 

 from dead gels lies in the fact that in the cytoplasm the junctions are continuously 

 reconstructed. The pattern of junctions in living matter is not rigid and 

 fixed as, for instance, in gelatin or still more in cellulose gels ; its only 

 permanent feature is its continual change ! 



The reconversion to the system of junctions proceeds according to- 

 some definite plan about which we remain completely in the dark.. 

 A temporary change in stability can also be produced artificially,, 

 owing to the thixotropic properties of the cytoplasm (see p. 66). By 

 mechanical means (pressure, shock) a reversible liquefaction can be 

 brought about. Such drastic interference is always followed, however.,^ 

 by a more or less serious damage to the cytoplasm (see p. 187). 



