FACTORS INFLUENCING BACTERIA 67 



is not due to heat but to the fact that the active light rays gen- 

 erate a poison within the cell. 



Rontgen and radium rays have little effect v^^hen allowed 

 to play directly upon bacteria. However, if the bacteria are in 

 living human tissue they are destroyed. The electric light in 

 time will kill bacteria, but microbes are much more resistant to 

 this than they are to sunlight. 



Electricity. — Can the little microbe be shocked to death by 

 the electric current as can man? It would seem from the 

 work which has been done that this is not possible. The pass- 

 ing of the electric current through a medium in which bacteria 

 are growing destroys many. This is due to the heat generated 

 and chemicals produced by the electricity passing through the 

 medmm. It is, therefore, something like it was with the in- 

 dividual who fell from a third-story window, and in telling of it 

 his friend said, "It was not the fall which hurt Pat but the 

 sudden stop.'' 



Electricity is used quite extensively today in the sterilization of 

 water and sewage and some have suggested its use in sterilization 

 of milk and other food products. The expense involved precludes 

 its extensive use at the present time. 



Shaking. — When subjected to the prolonged shaking of heavy 

 machinery bacteria are first prevented from multiplication and 

 later killed. This may be due to the actual breaking of the 

 cell to pieces by the violent shaking. However, it is well known 

 that the continuous shaking of some proteins will cause them to 

 coagulate. 



Osmotic Pressure.— If a perfume is liberated in one part of 

 the room its odor can soon be detected in any part of the room. 

 We thus find that gases tend to diffuse from points of high 

 concentration to points of low concentration. Similarly, if we 

 dissolve copper sulfate in water, place it in the bottom of a tall 

 cylinder, and cover with pure water, we shall find that as time 

 ffoes by the blue zone of copper sulfate creeps up into the clear 

 solution and in time the two solutions would be of uniform 

 concentration. Now, the force which is driving the copper sul- 



