MECHANISM OF DEATH 305 



Another experiment, with another strain, gave similar 

 results. The death rates are sufficiently constant to 

 obtain an average. From the equation on p. 281, the 

 percentage of survivors can be computed: 



100 



P = 



10 



0.434/5: 



= 77.1% at room temperature (16-18°C.) 

 = 86.1% in the refrigerator (6-8°C.) 

 = over 99.9% in liquid air (-190°C). 



This gives the death rates per unit time (=2 days) as 

 22.9%, 14.9% and less than 0.1% respectively. 



(6) OXIDATION AS THE CAUSE OF DEATH 



The possibilities for the cause of death by desiccation 

 are few. Catabolism is out of the question because it 

 requires moisture. It may be that the colloidal state 

 of the protoplasm is changed irreversibly and irreparably. 

 This does not seem probable because of the very slow 

 death-rate. Such a change might occur during the 

 drying process, and may cause death. After the 

 bacteria are once dry, and still alive, a colloidal change 

 is less probable. 



Another possibility is oxidation. Paul, Birstein and 

 Reuss (1910a) proved oxidation to be the main cause 

 of death of dry staphylococci. The bacteria were kept 

 in air (20.8% O2), in technical oxygen (96.2% O2), and 

 in mixtures of oxygen and nitrogen. Each of the death 

 rates in the following table is the average of 6-8 indi- 

 vidually determined constants. 



This table shows that the death-rate increases with 

 the oxygen concentration. The authors found that the 

 rate is proportional to the square root of the oxygen 



