ANHYDRIOBIOSIS 



27 



such as albumin (Table II). This finding also explains the con- 

 flicting results obtained with various protective colloids and 

 different bacteria when unequal concentrations of bacteria were 

 used for drying. 



As has been mentioned previously, the 'protective colloids' 

 perhaps diminish the number of deaths due to freezing alone : 

 but if the optimal proportion between bacterial cells and their 

 protective solution, for example Nal, has been established, the 

 addition of the colloid may only make the situation worse. 



In conclusion I should like to mention some possible practical 

 applications of these findings concerning the lethal effect of 

 oxygen on dried bacteria. 



Analysis of the curve of inactivation of dried cells of E. coli 

 by molecular oxygen or air (Fig. 6) indicated that the kilhng 

 effect was not a monomolecular reaction and that it resembled 



100 



0.01 



2 3 4 5 



Hours of exposure to air 



Fig. 6. Kinetics of inactivation of freeze-dried E. coli exposed to air. 

 Ampoules containing 1 ml of aqueous suspensions of E. coli, 

 B/r (1.5 • lO^Vml) were exposed to air at the end of freeze-drying, for 

 various periods of time. Curve A = experimental results; curve B = calcu- 

 lated on the assumption that as regards its lethal effect the concentration of 

 oxygen is reciprocal to the time of its action on dried bacteria (see text). 



References p. 29 



