289 



A liberation of ions on freezing has also been reported 

 by Dexter, Tottingliam and Graber (1930) who observed 

 a higher electric conductivity and a higher electrolyte con- 

 tent in frozen than in unfrozen plant sap, 



Fischer (1911) suggests that one of the modifications 

 caused by freezing in colloids might be a loss of their 

 power to absorb water. He attributes to this change the 

 ditference observed by some biologists in the quantity 

 of heat liberated during the freezing of a tissue and the 

 quantity of heat reabsorbed on thawing. 



Becquerel (1937, 1938, 1939)', considering the resem- 

 blance between a tissue killed by freezing and no longer 

 capable of holding its water and a gel which loses its 

 water when its structure breaks down (syneresis), pro- 

 poses the theory that death is a structural disorganiza- 

 tion identical with that occurring in such gels. He ob- 

 served in cells of the epidermis of the onion, immersed in 

 liquid air and thawed, a decrease of the volume of the 

 nuclei which could be interpreted as comparable with the 

 contraction of gels which lose their water by syneresis. 

 Becquerel then pictures death as follows : During freez- 

 ing (he speaks in particular of freezing in liquid air), 

 syncretic phenomena take place which consist in a sep- 

 aration of water from the rest of the colloidal system and 

 in an irreversible chemical change of the colloidal par- 

 ticles; on thawing, the particles so modified aggregate 

 into larger masses and form a coagulum. The fluid ex- 

 truded after thawing consists of the syncretic w^ater 

 and of the cell sap which easily traverse the now dis- 

 rupted protoplasm. 



Concerning the water-holding properties of living tis- 

 sues, it is interesting to compare them Avith those of 

 aqueous gels. Though these two systems might be quite 

 similar in many respects, they differ, among other fea- 

 tures, in their behaviour on freezing. As Jones and 

 Gortner (1932) have pointed out, when one freezes (rapid 

 freezing) a gelatin gel several times in succession, the 



