26 A. KOHN AND M. LION 



would react more easily with oxygen. In Szent-Gyorgyi's experi- 

 ments, riboflavin phosphate which fluoresced in the presence of 

 oxygen ceased to do so when certain substances, known as 

 fluorescence quenchers, were added. These protective substances 

 — KI, thiourea, cyanates, nitrites, etc.^ — which deactivate the 

 reactive state sensitive to the magnetic field of oxygen are indeed 

 the same that protect dried bacteria against the lethal effect 

 of oxygen. 



Why are cations such as Na+ and Li+ protective, while K+ is 

 not? Since the presence of crystalline water makes transition to 

 the triplet state more probable, any ion which interferes with the 

 formation of the crystal lattice should be protective, as indeed 

 is the case with Na+. In the case of cystein and glutathione, 

 which increase the lifetime of the metastable and reactive states, 

 one would expect enhancement of the oxygen effect, as is 

 actually observed. 



High mortality sometimes obtained on drying bacterial 

 suspensions of low density in isotonic solutions may be obviated 

 by adding more cells, alive or dead. Moreover, the same effect is 

 produced by adding certain proteins, i.e. 'protective colloids' 



TABLE II 



PROTECTIVE PROPERTIES OF SODIUM IODIDE AND ALBUMIN ON 

 LYOPHILIZED DRY CELLS OF E. CoU EXPOSED TO AIR'^ 



Cone. Concn. of Relative viability % 



Nal bacteria before No additives With 4% serum albumin 



/o 



drying A* B* A* B'^ 



A* At the end of drying. 



B* After an exposure to air for 220 min at 28' 



