•^.yj. 



method (tliird .uioup aboNc) we li;i\(' cxidciice from all 

 angles that it' cooling niid rcwai'iniiii;- are sufficiently 

 rapid to prevent the formation of ice and to really vitrify 

 protoplasm, life is preserved, while if a good vitrification 

 cannot be achieved, the damage is in proportion to the 

 degree of crystallization (for experimental data cf. our 

 review: ''The Physical kStates of Proto])lasm at Low 

 Temperatures"). Death then seems to result from the 

 disruption of the units which constitute living matter 

 when the molecules of water are torn away from these 

 units by the forces of crystallization, and the cause of the 

 innocuousness of low temperature seems to be the absence 

 of f reezable water. 



In this discussion of the three groups of cases in which 

 extreme cold is innocuous, we assumed, on the basis of 

 circumstantial evidence, that no ice was formed in the 

 protoplasm. We know, how^ever, only one direct obser- 

 vation of the actual absence of ice in protoplasm at very 

 low temperatures: Luyet and Thoennes (1938a) reported 

 that the plasmolyzed protoplasts of the cells of onion epi- 

 dermis do not lose their isotropic properties when im- 

 mersed in liquid air. 



B. Resistance to Extreme Cold and 

 the Structure of Living Matter. The 

 experiments on vitrification show that living matter can 

 be hardened into a solid without being killed. The passage 

 from the liquid to the solid state is not lethal. On the 

 other hand, the passage from the liquid to the crystalline 

 state at near-zero temperatures and the passage from 

 the solid amorphous to the crystalline state in devitri- 

 fication experiments is lethal. Now, the change involved 

 in the transformation of a liquid into an amorphous solid 

 is simply an increase in cohesion connected with a closer 

 approximation of the molecules, while crystallization in- 

 volves a rearrangement of the molecules. The struc- 

 ture of living matter is, therefore, such that life is com- 

 patible with the increase in compactness and density 



