SUMMARY 215 



ism, attack and invasion by other organisms, can be 

 greatly reduced if not entirely prevented by general hy- 

 giene and by medicaments which may also be employed 

 in treating individual cases of disease. In extreme cases 

 surgery must be resorted to for removing a diseased part 

 which might if neglected involve the whole. Insects, 

 fungi, and bacteria are the principal causes of plant, as 

 well as of animal, disease. 



