SUNSHINE AND LIFE 77 



sideration in regard to the effective insolation of 

 water is its chemical composition, for it has been 

 shown * that the action of sunshine in destroying 

 germs in water is very considerably increased 

 when common salt is added to the water, and 

 this opens up a wide field for experimental 

 inquiry before we can accept sunshine as a 

 reliable agent in the purification of water. 



Again, we must remember that a great deal 

 depends upon the condition of the microbe itself. 

 If it is present in the spore or hardy form, then 

 considerably longer will be required for its an- 

 nihilation. This fact has been abundantly shown 

 in the case of anthrax, which in the condition 

 of spores will retain its vitality in water flooded 

 with sunshine for considerably upwards of a 

 hundred hours, the bacilli being far more easily 

 destroyed. We must also bear in mind that the 

 individual vitality of the microbe is an important 

 factor in determining its chance of survival ; if 

 it is in a healthy, vigorous condition, it will resist 

 the lethal action of sunshine for considerably 

 longer than when its vitality has been already 

 reduced by adverse surroundings. 



It is, therefore, sufficiently obvious that the 

 power of insolation to bacterially purify water 



* PERCY FRANKLAND, Our Secret Friends and Foes, 4th 

 edition, p. 188. 



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