221 



Experiments like those just described were also carried 

 out with the spermatozoa of tlie ral, but not a single one 

 could be revived. 



Goetz and Scott-Goetz (1938) described experiments in 

 which yeast previously treated by the vitrification methods 

 was killed when exposed, in monocellular layers, in a wire 

 loop, to temperatures of some few degrees below zero, 

 while it was intact when exposed, under the same condi- 

 tions, to 150° below zero. This seems to indicate that the 

 very low temperatures, at which the vitreous state can be 

 maintained, do not kill, while the higher temperatures 

 which cause devitrification are lethal. 



The epidermis of the onion, a classical subject in plant 

 cytology, seemed to be particularly appropriate for our 

 researches, especially because of the ease with which one 

 can obtain very thin monocellular layers (Luyet and 

 Thoennes, 1938b). A piece of epidermis, held on a small 

 metal fork, was immersed into liquid air and then into 

 water at 20°. The vitality of the cells was tested by plas- 

 molysis. A first series of observations furnished only 

 dead cells. Thinking that the quantity of water present 

 in the large vacuoles of the epidermal cells rendered vitri- 

 fication impossible, we tried to reduce this quantity of 

 water by plasmolysis in salt solutions. No cell could be 

 revived. But we had not taken account of the fact, re- 

 ported by many investigators, that a direct immersion in 

 water after plasmolysis in a concentrated salt solution is 

 often fatal. The invasion of the strongly plasmolysed cells 

 by water produces a too violent expansion which causes the 

 bursting of the protoplast. We therefore tried to warm 

 tlie cells rapidly by immersing them not directly into water, 

 but into a saline solution at 20°. This time we found a 

 considerable number of cells capable of being deplas- 

 molysed or plasmolysed to a further extent. 



A study, with polarized light, of the plasmolysed onion 

 epidermis, in liquid air, showed that the cellular proto- 

 plasm, concentrated by plasmolysis, was isotropic, while 

 the space which surrounded it and which contained only 



