xviii CONTENTS 



PAGE 



Impairment Due to Alteration of Normal Metabolism 186 



Neurasthenia 186 



Direct Treatment of Nervous Disorders 187 



Treatment of Nervous Disorders by Psychotherapy 187 



Malnutrition 188 



Poisoning 189 



Disease Due to Mechanical Injury 189 



Section 5. Association of Organisms 



CHAPTER XVIII 

 Association op Organisms 



Nature of Association 193 



Family (Iroups, Herds 194 



Bee Colonics 194 



Ants 195 



A Comparison, Ant and Man 195 



Symhioscs, Definition 196 



Commensalism, or Messmatism 196 



Parasitism 198 



Parasitic Plants 198 



Animal I*arasitos 199 



Structure of Parasites 201 



Degeneration 202 



Life Histories 202 



Effects of Parasites on Host 203 



CHAPTER XIX 



DisEASKs OF Plants 



Economic Importance of Plant Disease 204 



Causes of Disease 204 



The Soil 204 



Tillage 206 



Polluted Air 205 



Moist and Dry Air 205 



Heat and ("old, Light and Shade 206 



Fasciation 207 



The Living Causes of Disease: Infections 207 



Worms 208 



Flics 208 



Pine Calls 209 



Thrips 210 



Fungi 210 



Nature of Diseases Due to Fungi 210 



The Rusts 211 



The Mildews 211 



Smuts 212 



Bacterial Infectious 212 



