l6o PLANT DISEASE 



I contend that it is a natural law that these 

 two forms of life are always more or less at 

 war, or in other words, nature is always destroy- 

 ing that which is imperfect. And just as there 

 are insects like the aphides which 'can destroy 

 plant life that has more vitality than, for 

 instance, the orange tree when attacked by 

 scale, so also there are bacterial or fungoid dis- 

 eases of animal life which can attack this life 

 when the vitality is only lowered below the 

 normal, while others are only deadly when the 

 vitality is at its lowest ebb. 



The higher form will always be able to resist 

 while its chlorophyll or haemoglobin is within 

 a given number of points of normal, the viru- 

 lence of the attack varying as the number of 

 points decrease from the normal and the range 

 of normality varying according to the attack- 

 ing force. 



From this I draw one conclusion : that if we 

 keep the higher forms of life at something 

 approaching normality, they will be immune 

 or impregnable to the attacking force. 



