123 



Jaccard and Frey-Wyssling (1934) reported a sharp 

 rise in the freezing point of the tissue of the root of Daucus 

 carota after the first congelation, hnt this rise was followed 

 by an irregular drop in subsequent freezings. In pieces 

 killed by heat, the freezing point remained constant. They 

 attribute the rise in the freezing point at the second freez- 

 ing to the fact that the water extracted from the cells during 

 the first freezing dilutes the extruded sap around the ther- 

 mocouple, which they used in their determinations. Wal- 

 ter and Weismann object to this interpretation, claiming 

 that the water extruded should be reabsorbed if the tissue 

 is still alive as Jaccard and Frey-Wyssling assume. 



According to Luyet and Gehenio (1937), the freezing 

 point of living potato tissue is, on an average, by as much 

 as 1.5 degree lower than that of dead material. In a ten- 

 tative explanation of this difference, they distinguish three 

 kinds of water in protoplasm: 1. water which acts simply 

 as a solvent in the cell sap, 2. water which behaves as a 

 protoplasmic constituent, 3. water which, in dead as well 

 as in living matter, is bound in such a way that it cannot 

 freeze; and they attribute the higher freezing point in 

 dead tissue to the fact that, at death, protoplasmic water 

 is transformed into solvent, readily-freezable water. 



This assumption, however, does not seem to be tenable 

 in view of new findings of Gehenio and Luyet (unpub- 

 lished) that protoplasm which has no cellular structure, 

 like that of the myxomycetes {Physarum polycepJialum), 

 does not present the difference observed between living and 

 dead tissues. So, finally, the lower freezing point of living 

 tissues seems to be due not to a binding of water in a proto- 

 plasyyiic structure but to a hindering of the water activity 

 by a cellular structure, probably the cellular membranes. 



Jensen and Fischer (1910) observed that the freezing 

 point was lower in dead than in living muscle. They 

 attribute this fact to some binding of water at death. 



Influence of Cooling Velocity on Freez- 

 ing Point s. The use of a high cooling velocity has 

 been found by many investigators to result in a lowering of 



