Chapter VIII — 133 — Active Relations 



After study and review of existing data, Luyet and Gehenio (1937) favor 

 the theory that the first freezing point represents the congelation of inter- 

 cellular liquid ; the second is due to freezing of the intracellular water. 

 Also confusing the attempt to interpret freezing behavior of living tissue 

 is the fact that variation of experimental conditions will produce different 

 results. Luyet and Galos (1940) studied the effect of rate of cooling on 

 the freezing point of living and dead potato tuber tissue, concluding that 

 the difference between the two values became less with decrease in cooling 

 rate, and suggesting that at a velocity of about 0.1° C. per minute, the two 

 should be approximately equal. Dead tissue did not behave in this manner. 

 This confirmed earlier results of Walter and Weismann (1935), who 

 state that while the freezing point of living tissue invariably is lower than of 

 dead tissue, no conclusions should be drawn from this as to the osmotic 

 concentration of the cell sap in living and dead tissue. They attribute the 

 discrepancy to the impossibility of stirring in such determinations, and to 

 the varying speed at which ice is formed. The latter in turn depends on 

 the permeability of the protoplasm to water, and on the DPD of the cells, 

 since freezing first occurs in the intercellular spaces. They present data 

 to show that under the same freezing conditions the same amount of ice 

 formed in living as in dead tissues, and that the osmotic pressure of the 

 cell sap is the same in both. This conclusion was necessitated by the ob- 

 servation that when cooling curves indicated an equilibrium between the 

 tissue and cooling bath, the areas under the two curves were the same. 

 Walter and Weismann's data are criticized by Levitt (1941) as not 

 conclusive, since it was not determined whether the tissue was alive at the 

 end of the experiment, a doubtful assumption in his opinion. 



Contrary to results obtained with tissues as experimental material, 

 Gehenio (1941) reported a higher freezing point for living myxomycete 

 Plasmodium than for dead. No adequate explanation seemed possible. One 

 suggestion was that freezing caused the disintegration of protoplasm with 

 the reduction in the size of particles and an increase in their number, thus 

 augmenting the effective concentration. The phenomenon might also be 

 explained by the preferential adsorption of water by the dead protoplasmic 

 colloids. 



There is better agreement between the freezing points of dead tissue and 

 expressed sap, although the former yields lower values. This has been 

 variously interpreted ; according to some (cf. Jaccard and Frey-Wyssling, 

 1934), it is due to the liberation of colloidally bound water, or to some other 

 type of disintegration or disturbance such as ruptured xylem vessels. With 

 this "dilution theory" Walter and Weismann disagree, pointing out that 

 cryoscopy of dead tissue, as of living tissue, is less accurate than of ex- 

 pressed sap because of the impossibility of stirring, etc. ; but when special 

 precaution is taken the two values agree well. Their view, then, is that the 

 concentration of cell sap remains constant throughout the living, dead, and 

 expressed sap states. 



In this connection tests carried out on beet root tissue may be of interest 

 (Currier, 1944a). A mercury thermometer with a small (5 mm. diameter) 

 bulb, and calibrated in fiftieths of a degree, was used. A small hole in a 

 tissue cylinder accommodated the bulb. Freezing was initiated by inserting 

 a small glass capillary filled with ice into the tissue. After the freezing 

 point of the living tissue had been determined, the cylinder was frozen, and 

 the freezing point of the dead tissue was ascertained in a similar manner. 



