552 RADIATION BIOLOGY 



the preliminary thermal and mechanical treatment of the substances. 

 It is also dependent on the substances administered and on time. More- 

 over, in thread colloids the viscosity increases with the length of the chain 

 molecules. Because protoplasm contains both spherical and thread col- 

 loids, its viscosity is dependent on all these properties. 



If, on the other hand, the view held by Seifriz (1936, 1942), Frey- 

 Wyssling (19-1:8), and others is adopted, i.e., that the protoplasm not only 

 is an amorphous system of colloids and solutions but also possesses an 

 internal structure, additional factors will affect the viscosity. According 

 to this conception, the principal components of the protoplasm, the pro- 

 tein molecules, are either joined into a framework by means of their side 

 chains or first joined into bundles (micelles). The latter in turn build 

 up the framework, to which enzymes, lipids — including phosphatides — 

 inorganic groups, water dipoles, etc., may be attached. The spaces in 

 the framework — the intermicellar spaces — are filled with water and with 

 substances dissolved and dispersed in it. These interpretations have not 

 been refuted by the observations of the structure of the protoplasm 

 hitherto made with the electron microscope (e.g., Mudd, 1947). 



Local concentrations in the framework may cause the occurrence of 

 microscopically visible fibrils and other corpuscles. Corresponding local 

 dilatations in the interstitial spaces can give rise to vacuoles and to 

 droplets. The fibrillar and the alveolar hypotheses were based on the 

 occurrence of such morphological differentiations. 



If this hypothesis for the plasmatic structure is accepted, it implies 

 that the viscosity of the protoplasm is conditioned not only by the vis- 

 cosity of the interstitial fluid but also by the plasticity and elasticity of 

 the framework. 



It can be assumed, on the foregoing premises, that the viscosity of the 

 protoplasm is a more complicated phenomenon than the viscosity of solu- 

 tions and colloids in general. The viscosity of the protoplasm will then 

 be the aggregate of the viscosity in its solutions and colloids (the dis- 

 persion viscosity) and of that caused by the junctions of the elements 

 in the framework (the structural viscosity). Frey-Wyssling (1948) 

 assumed that the protein molecules and the other components of the 

 plasmatic framework are united by different kinds of valence bonds and 

 cohesive bonds. He also assumed that the framework can be successively 

 or partially dissolved and reunited by means of the breaking and joining, 

 respectively, of these bonds. Conseciuently, the physical properties of 

 the protoplasm (fluidity, plasticity, and elasticity) may be attributed to 

 the characters of the various junctions. The more these are dissolved, the 

 more liquid the protoplasm becomes; i.e., its viscosity decreases. Thus, 

 because the structural viscosity varies with the joining and breaking of 

 the bonds and the dispersion viscosity is constantly affected by the 

 changes in the factors enumerated in the foregoing, the viscosity of the 



