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the water phase is separated by freezing- from the proto- 

 phisniic substance. 



Some authors, after Klemm (1895), have observed that 

 freezing causes a granulation of protoplasm. The mech- 

 anism of this alteration, which is probably physiological 

 in nature, is unknown. 



Freezing might be more injurious to some vital activi- 

 ties than to others and destroy one particular function 

 before it destroys them all at death. This assumption 

 w^ould explain the observation of Pictet (1893) that a 

 wound made by freezing takes a much longer time to heal 

 than a wound inflicted by other injurious agents. The 

 subepidermal tissues would have lost their powder of re- 

 geueratlug the dead portion. 



2. Physical and Chouical Changvs. Most of the phy- 

 sical changes assumed to take place at freezing tempera- 

 tures are phase separations. The most important phase 

 separation is evidently that of water; but other phases 

 might separate either directly when a saturation temper- 

 ature is reached or indirectly as a result of dehydration. 



Gorke (1907) assumed that the proteins dissolved in 

 the cell sap of plants might precipitate at death, such a 

 precipitation being due to the gradually increasing con- 

 centration of the sap subsequent to the withdrawal of 

 water by freezing. He attempted an experimental study 

 of his theory by determining the amount of precipitable 

 protein in the sap extracted from previously frozen and 

 from unfrozen plants. The proteins w^ere salted out and 

 the nitrogen content of the precipitate was determined by 

 the Kjeldahl method. The sap from frozen material 

 contained only 2/3 the quantity of nitrogen found in the 

 sap from living plants. Unfortunately Gorke 's proce- 

 dure is subject to criticism (as Voigtlander, 1909, pointed 

 out) in the fact that he extracted the sap by a slight 

 pressure in frozen tissue, in which the fluid came out 

 readily, wdiile he crushed the living tissue; this differ- 

 ence in treatment might well account for the difference 



