CHAPTER VIII 

 MICROORGANISMS 



431. Microorganisms. We have seen in the last chapter 

 (Arts. 377 to 380) that every living thing, whether animal 

 or plant, requires energy with which to carry on its life proc- 

 esses. We have seen also that energy is derived directly by 

 living organisms only from certain very complex chemical 

 compounds which we call foods. Again, we have seen that the 

 only living organisms which have the power of manufacturing 

 these foods out of the relatively simple materials found in the 

 soil and air are the green plants (Art. 380) . Every substance 

 in the world which is capable of serving as energy-giving food 

 for a living organism has derived its energy-giving power either 

 directly or indirectly from a green plant. Thus, the green 

 plants are the food makers of the world and all other organ- 

 isms are dependent on them for nourishment. Since this is 

 true, it is easily seen that all animals and all non-green plants, 

 such as molds, yeasts, and bacteria must be constantly com- 

 peting with each other for possession of the food that comes 

 either directly or indirectly from the green plants. Every 

 one is familiar with the fact that animals in general consume 

 essentially the same kinds of food as man does. Corn, wheat, 

 and oats are food for the lower animals as well as for man. 

 Birds, mice, insects, and other wild animals do not hesitate 

 to help themselves to the food that man has provided for 

 himself and for his domestic animals. 



432. Plants That Attack Our Foods. People in general, 

 however, are not so familiar with the fact that the worst com- 

 petitors which man has for possession of the food which he 

 wishes to preserve, are the non-green plants. We are all 



