MECHANISM OF DEATH 



371 



For this reason, the order of death by depressed surface 

 tension would be very enlightening, but no data about 

 this are known to the author. 



IX. DEATH BY LIGHT 



It is an old experience that bacteria are killed by 

 light and also by rays of shorter wave lengths. The 

 order of death is usually logarithmic. Table 117 gives 

 the data obtained by Lee and Gilbert (1918) on the 

 death of Bad. coli by the light of a 100 Watt lamp. 

 The death rate is a decreasing one and indicates an 

 heterogeneous culture. 



Header (1926) calls attention to the fact that only 

 certain wave lengths of the sunlight will kill bacteria, 

 and that the action of sunlight is different at different 

 times of the day. 



Two causes of death are possible: either the rays 

 act upon the cell, or they act upon the medium, producing 

 in it harmful substances, as, e.g., H2O2. In this latter 



Table 117. — Death of Bad. coli by the Light from a 100 



Watt Lamp 



