ROUND TABLE DISCUSSION 211 



unless protected by special substances, the micro-organisms are 

 killed in the dry state by oxygen. The hypothesis we proposed 

 regarding the mode of the action of the oxygen invokes the 

 paramagnetic properties of the molecule. Whether the hypo- 

 thesis is valid in regard to micro-organisms other than those we 

 have used, let alone other systems, remains to be learnt. 



Moderator: Do you consider, Dr. Lees, that given the proper 

 techniques all forms of life could remain viable when desiccated, 

 as is the case with micro-organisms? 



Lees: No, I think that most multicellular animals would 

 succumb to complete desiccation. The explanation may have 

 been provided by Prof. Halvorson when he emphasised the 

 importance of structure in preserving viability. Desiccation 

 leads to irreversible structural changes. 



Moderator: Should we perhaps assume then that there has 

 been in certain organisms a specific evolution of a mechanism 

 which prevents structural injury on desiccation? 



Lees: It would seem so. Although the extraordinary Chiro- 

 nomid PoIypediJwn vanderphnki obviously shrinks on desicca- 

 tion, it must have some means of preserving essential structures 

 from damage. In this respect it is almost unique: other species 

 of bloodworms die as soon as they have lost about three 

 quarters of their body water. 



Halvorson : I would like to quote here the results of some 

 experiments we performed in our laboratory some time ago. We 

 measured the moisture affinity of some vegetative cells and in 

 spores. This was done by measuring the equilibrium vapour 

 pressure of the moisture in spores and in vegetative cells at 

 different stages of drying. We found that in spores the vapour 

 pressure remained close to that of pure water, until nearly all 

 of the water had been removed, but in the vegetative cells the 

 equilibrium vapour pressure fell rather rapidly while the 

 moisture content was still relatively high. This would indicate 

 that in the spore the water is free, that its removal does not 

 affect the structure, and that there may be relatively little 

 shrinking in a dry spore compared to a wet one. In vegetative 



