242 



niul which, in ihc dry stale, an- ii(»l atVcrtcd l)y the ht\v 

 temperatures in question; '2. Thox- which, either with 

 tlieir full water content or after luniiii;- been only slio-htly 

 dehydrated, are innnune against cxtrenu' cold. This sec- 

 ond class, in its turn, includes two subdivisions: 1. There 

 are organisms which survive liquid air temperatures only 

 when special precautions are taken, such as extremely 

 rapid cooling- and re warming; '2. There are others which, 

 without any of these precautions, can be immersed in 

 liiiuid air, liquid hydrogen or iiiiuid helium without in- 

 jury. The experimental data concerning these three 

 groups are presented in tables 2, 3 and 4. 



2. Discussitni. A. C a u s e o f the K e s i s t a n c e 

 t o K X t r e ni e C o 1 d. The fact that all the organ- 

 isms mentioned in the tirst grou]) (Table 2) resist very 

 low temperatures when they art' dried suggests that it is 

 the absence of freezable water which innnunizes them. 

 The type of precautions which save the organisms of 

 the third group (Table 4) from death, that is, rapid cool- 

 ing and rewarming through the temperatures at which 

 freezing of water would be i)Ossible (from to some tens 

 of degrees below ), supports the assumption that, if 

 ice formation is prevented, danger is avoided. This as- 

 sumption has naturally been applied to the organisms of 

 the second group (Table 3), in other words, it has been 

 thought that when bacteria, yeasts, fungi, algae, ]irotozoa 

 and germ cells in the vegetative state or nematodes, ro- 

 tifers and tardigrades, with their full water content, re- 

 sist innnersion in Tuiuid air, it is because their water does 

 not freeze. 



The cause of the assumed absence of ice in the organ- 

 isms of the second group has been sought in the capillary 

 forces within the intermicellar spaces. Some types of 

 protoplasm (the bacteria, in particular) w^ould be of a 

 denser structure and the capillary spaces in them would 

 be so small that '"water Avill not be changed into ice at 

 any temperature" (Lipman, 1939). Concerning this view 



