l-jZ FINE-STRUCTURE OF PROTOPLASM II 



(p. 1 86). If a gel is liquefied under isothermal conditions, the volume 

 can either increase (gelatin, agar) or remain constant (Na-oleate and 

 other thixotropic gels) or decrease (methyl cellulose in water), A 

 decrease in temperature or an increase in pressure favours gel form- 

 ation in the first case and sol formation in the third (Freundlich, 

 1937). Cytoplasm belongs to the third category (p. 187).^ In addition 

 and in contrast to all other gels, it can also change its aggregate state 

 by itself, even if the external physical conditions remain unaltered. 



It seems that anaesthetized cytoplasm is more gelated than in the 

 active state, as Seifriz (1950) finds that any anaesthetic causes a 

 reversible gelation of protoplasm. 



We are thus faced with the paradox that cytoplasm simultaneously 

 exhibits the characteristics of hquids (fluidity) and of solids (elasticity). 

 It is noiv solid, then liquid to an extent rarely observed in any other 

 colloid. The task of submicroscopic morphology consists, therefore, 

 in drawing up a structural scheme which explains the double nature 

 of cytoplasm at the boundary of the two classical aggregate states. By 

 doing so, we should gain more than by adhering to the concept of 

 cytoplasm either as a liquid or as a gel, neither of which can be true 

 in a general sense. 



d. Submicroscopic Structure of Cytoplasm 



Particulate globules. If we disregard the microscopic inclusions in 

 cytoplasm (plastids, mitochondria, lipid globules, granules etc.), it 

 represents a microscopically homogeneous pseudophase. This is no 

 longer true when it is observed in the electron microscope, where 

 submicroscopic particles appear to be dispersed in a reticulate, fiorous 

 or homogeneous matrix of diameters from 5 00 to 1 5 00 A (Claude, 

 1946; Faure-Fremiet, Bessis and Thaureaux, 1948; Lehmann, 

 1950). In liver cells these particles are distinctly smaller than the mito- 

 chondria, which measure 2000 to 5000 A. Claude suggested calling 

 them "microsomes". Globules of 1000 A diameter may lodge as many 

 as 64 of the biggest macromolecules listed in Table XV (p. 141), so 

 the microsomes must contain a great number of protein molecules and 

 other compounds. 



According to Bensley (1943), the submicroscopic particles, isolated 

 from homogenized liver tissue by the centrifuge, consist of protein, 



^ Brown (1934) and Marslakd (1942) have checked this up to 1000 atm. 



