224 J. E. Lovelock 



diffuse away. In a medium maintained continuously un- 

 saturated with respect to the lipid components of the cell 

 membrane this process will continue until so much of the 

 lipoprotein has unravelled that the intact existence of the cell 

 is no longer possible. The increase in the rate of haemolysis 

 below 5° could result from a hardening of the cementing lipids, 

 if the repair of small breaches in the membrane depended on 

 their ability to flow. Recent investigations of the effects of 

 thermal shock on red cells suggest that such a hardening of the 

 lipids may in fact occur (Lovelock, 1955b). 



The free energy of the lipid components of a highly organized 

 structure such as the red cell membrane is likely to be higher 

 than that of the same components in their saturated solution. 

 It follows that the red cell membrane is probably unstable in a 

 physical sense, and its intact existence may well depend upon 

 the continuous synthesis of lipid components, and upon the 

 presence of a considerable reserve of membrane material. 



The effects of cold storage 



The experimental evidence so far shows that the red cell 

 will disintegrate rapidly if kept in a medium which is not 

 saturated with the components of the cell membrane. In 

 their normal environment and during cold storage in their 

 plasma the cells swim in the presence of a considerable excess 

 of lipid and possibly other membrane components; in these 

 circumstances it might be thought that damage by diffusion 

 would not take place. The chemical analysis of red cells, after 

 storage for a few months at 20°, indicated that changes very 

 similar to those following exposure to alumina take place 

 (Lovelock, 1954). Unless a physiologically abnormal medium 

 is used for their storage, namely one which is acid and which 

 contains a salt such as sodium citrate or lactate, a rapid dis- 

 solution of the cells takes place. The beneficial effects of the 

 acid citrate medium used for the routine cold storage of red 

 cells are directly attributable to its poor solvent action towards 

 stroma lipoprotein. 



Even in this medium, however, adverse changes do occur 



