2G4 



atui't', tlic imiiihci" ol' (•rys1;iHr/.;it ion cciilcrs t'oi'iiird and 

 llit'ii- \('l()t'it>- of i;i-()\vtli. Bui llic pari of this suggestion 

 concerning tlie i)ossibility of avoiding injury ])y causing 

 the formation of sniallei- crystals could not l)e conlirnied 

 ex])erinientally, as the following observations show. 



lljin ( IJ'.'U), after comparing exix'riiiiciits on rapid 

 and slow cooling of the cells of red cabbage leaves, con- 

 cludes that sudden freezing is more injurious than slow 

 freezing. 



The abrupt iunuersiou of sticklebacks in li(|uid air by 

 Weigman (IK.'Ui) killed the animals readily. 



Identical experiments by Luyet (1938) on gold lish gave 

 the same results. 



Luyet and Thoennes (1938a) found that monocellu- 

 lar layers of plant ej)! dermis presented only dead cells 

 after rapid freezing in li(]uid air. 



As is evident, these experiments which do not confirm 

 the idea of a lesser injurious effect of smaller crystals, 

 do not invalidate the theory of a possible mechanical 

 injury on protoplasmic structure by ice. 



Some have thought that a mechanical contact with ice 

 might result in a coagulation of protoplasm, since it is 

 well known that touching or piercing wdth a needle 

 (Chambers) or i)ricking a cell may result in its coagula- 

 tion. Lepeschkin (1936) apparently follow^s this trend of 

 thought, when he speaks of "mechanical coagulation" by 

 freezing. 



C. The killing of protoplasm under the action of the 

 pressure exerted by the expanding ice is often referred to 

 in the biological literature. Among the authors who dis- 

 cuss this theory more extensively let us mention Plateau 

 (1872) who attempts to show that there is no pressure 

 within the ice in formation. It is a known physical prin- 

 ciple, according to him, that the cavities in a solid body 

 expand like the body itself. Therefore the cell contents 

 cannot be crushed by the freezing of the tissue around 

 them. He claims to liaxc shown Ihe al)sence of pressure 



