22 



A. KOHN AND M. LION 



carried out on two strains of E. coli, which were osmotically 

 stable enough to withstand suspension in distilled water; some 

 experiments were done on other Gram negative bacteria. 



He found that the process of drying itself was quite innocuous 

 to bacteria (even though suspended in water only), as long as 

 they did not come into contact with air, or rather oxygen 

 (Fig. 4). 



When an inert gas such as hydrogen or nitrogen was introduced 

 into the dried material, the bacteria were preserved in a viable 

 state as if sealed in vacuo. The lethal effect of air was proportional 

 to its oxygen content, or to the partial pressure of the oxygen, 

 and there was a reciprocal relation between the pressure of the 

 air acting on the dried bacteria (in the range 50-760 mm Hg) 

 and the time of exposure needed for inactivation. 







D 

 t- 

 0) 



X> -1 



D 

 XI 



H- 

 O 



-E -2 

 n 



D 



> 



o 



12 3 4 



Hours of exposure to air 



Fig. 5. Protective properties of components of Naylors medium-'- on 

 freeze-dried E. co// exposed to air. 1-ml suspensions of £". coli in the following 

 media were exposed to air at the end of freeze-drying. Curve A = control 

 in vacuum; B = full Naylor's medium; C = thiourea 1 %; D = thiourea 

 0.5%; E = ammonium chloride 0.5%; F = sodium ascorbate 0.5%; 

 G = distilled water; H = dextrin 2%. 



