177 



tare (hreakiiig down which results in the liberation of the 

 proteins) rather than to the duration of the solving pro- 

 cess. The increase in volume after a relatively short 

 time in the frozen state (under 4, above) is attributed 

 tentatively to the destruction of the capillary structure and 

 to a reduction of capillary pressure. The decrease in vol- 

 ume on thawing- (under 1 above) is more puzzling since a 

 precipitation of the dissolved protein would increase the 

 volume. Moran suggests that a process comparable to 

 the swelling of proteins, which is known to result in a final 

 shrinkage of the entire mass in which they are held, takes 

 place in the precipitated flakes of the yolk. The decrease 

 in volume during subcooling (under 3 above) is ascribed to 

 an increase in the quantity of bound water, the degree of 

 hydration of stable hydrates tending, in general, to in- 

 crease at lower temperatures. The suggestion is made, 

 finally, that this decrease in volume, observed in the sub- 

 cooled state, might be the beginning of the same decrease 

 which was observed after thawing, and which could even- 

 tually become an irreversible change if subcooling were 

 maintained long enough. 



Moran reported also that the irreversible changes just 

 mentioned do not take place when the yolk is frozen in 

 presence of a lOYc sucrose solution (at -11°). He com- 

 pares this phenomenon to what happens in plants which 

 are rendered winter-hardy by an increase in their sugar 

 content. (Such protective action, according to Shrivas- 

 tava {J. Phijs. Chem. 29, 166, 1925), would be due to an 

 adsorption of sugar on colloidal particles.) 



The permanent modifications produced in yolk by 

 freezing w^ere studied microscopically. Normal untreated 

 yolk, fixed in Miiller's fluid, consists of polygonal masses 

 (the yolk particles). Frozen yolk, fixed in the same man- 

 ner, presents a horny appearance. The author explains 

 this by a rupture of the yolk particles on freezing, a 

 rupture which can be obtained also by stirring. 



Nord (1927-1938) and his collaborators investigated 

 the effect of freezing, for various lengths of time, at tern- 



