CHAPTER LXV 

 THE CONFLICT OF LIFE WITH LIFE 



395. The predatory relations. Many of the animals, and 

 most of the plants, that are incapable of manufacturing their 

 own organic food get their food from the bodies of other plants 

 or animals that are already dead. But there are very many 

 animals, and a few plants, that kill their prey. 



The gentle cow and the soft-eyed deer browse on the 

 herbage, and we never think of them as beasts of prey ; yet 

 from the point of view of the grasses and shrubs that furnish 

 them their food these animals are truly predatory. That is to 

 say, they are direct destroyers of living things. To maintain 

 themselves upon this earth, certain living things must somehow 

 protect themselves against predatory enemies, and this is just 

 as true of plants as it is of animals. 



396. The parasitic relation. There are many plants and 

 animals that get their food supplies from the living bodies 

 of other organisms. That is to say, they eat from the living 

 victim, sometimes thereby killing, but not always and not 

 necessarily. Plants and animals that get their food in this 

 way are called parasites. 



The most common parasites are found among the lowest 

 plants and animals ; but nearly every class of living things has 

 its parasitic representatives. Some two dozen of the common 

 diseases of man, and many diseases of our domestic animals, 

 are known to be caused by the activities of parasitic bacteria 

 in the bodies of the victims. Protozoa as parasites are known 

 to cause malaria and the sleeping sickness of Africa. Most 

 of our common plant diseases are caused by fungi or bac- 

 teria. The hookworm is a serious parasite on man ; and the 



