isn 



whicli were ]tr('\iously frozen ;»1 about -80° and thawed, 

 found that tlu' colhihir constituents couhl ])e stratified 

 without ditlfic'iilty wliih' in tissues killed by heat no dis- 

 placement was possible. Accordingly, they think that 

 freezing does not induce protoplasmic coagulation as read- 

 ily as do other lethal agents, such as, heat, toxic substan- 

 ces, high pressure, radiations, mechanical injury, etc. This 

 is confirmed by the absence, in frozen tissue, of the char- 

 acteristic opacity observed in tissue killed by the other 

 methods. 



However, Luyet and (libbs (1937) published photomicro- 

 graphs sliowing tiie ])rotoplasm coagulated in frozen and 

 thawed plant epidermal cells. The pattern of this coagu- 

 lum was different than that obtained in death by heat. 

 The authors remarked a difference in the consistency of 

 the two types of coagula, which might explain why the com- 

 l)onents of one type could be separated by centrifugation 

 while the components of the other could not. The coagu- 

 lated material was found in a thin layer adhering to the 

 wall of the cell in the same position as in the living state. 



Bugaevsky (1939) also observed coagulated flakes in the 

 cells of wheat after freezing and thawing. 



The tearing of cell membranes by ice has been assumed 

 by the earliest biologists. Goeppert (1830) contended that 

 he could never observe any broken membrane. After him 

 several authors have contributed to establish the fact that 

 there is never a perforation of the membranes by ice crys- 

 tals (for quotations see above, under the title "Phase 

 Separation" in tissues). But, if the membranes are not 

 broken, it is cei'tain that they are damaged and that they 

 lose their semipermeability, as is evidenced by the fact 

 that the cellular fluids cannot be maintained any more 

 within the cells and that the penetration of dyes becomes 

 considerably easier. Prillieux (1869a) however, con- 

 tended that there is more evidence for an injury to proto- 

 plasm than to its membranes. 



Matruchot and Molliard (1902) reported the particular 

 phenomenon of the vanishing of the chromosomes in a 



