283 



be reabsorbed after Ihawiiio-, death can be prevented. 

 Concerning- this (lueslion, a remark of Stik'S (quoted by 

 Jones and Gortner, 1932) is of interest. Hydrated gela- 

 tin h)ses 4 to 6 times more water on thawing when it 

 has been frozen slowly than when it has been frozen 

 rapidly. Jones and Gortner (1932) mention, as a natural 

 explanation of this observation, the fact described by 

 Moran (1926) and by Hardy (1926) that, in rapid freez- 

 ing, a large number of small crystals are formed within 

 the gelatin mass and a reabsorption of that water after 

 thawing is easy and rapid, while, in slow freezing, the 

 presence of larger quantities of ice at the same place 

 and mostly at the external surface impairs or slows 

 reimbibition after thawing. 



A determination by Luyet and Condon (J9S8) of the 

 time at which the cells of potato tubers are killed when 

 gradually increasing proportions of water are with- 

 drawn by freezing, led these authors to the conclusion 

 that injury begins after the withdrawal of about 35% of 

 the water content, at a temperature of 0.2 to 0.3 degree 

 below the freezing point (between B and C in the graph) 



Fiu. 33. Freezing curve of a piece of potato. Abscissae: time in min- 

 utes from the beginning of freezing; Ordinates: temperature. During 

 the periods of time indicated by A and B no ceH was kiUed; death oc- 

 curred during the period C; freezing continued when all the cells were 

 killed, during the period D. (From Luyet and Condon, 1938.) 



and that all the cells are killed when about 70' < of the 

 water has been removed at 3.5 degrees below the freezing 



