OFFSPRING OF SIMPLE ORGANISMS 17 



is a single cell, but their great numbers make up for their 

 smallness. The green substance in them enables each 

 individual cell to manufacture organic food out of the 

 inorganic materials that come to it. 



Other plants, as the bacteria, are not green and have 

 not the pow^er of making starches and sugars, but they 

 have other powers equally important. They must get 

 their food chiefly by attacking other plants and animals, 

 either after they are dead or v^hile they are still alive. 

 Those organisms which live at the expense of other living 

 things we call parasites. 



Finally, we have a great many animals that are one- 

 celled in their structure. These are like the bacteria in not 

 being able to make their own food. They depend on other 

 organisms living or dead. They are, however, usually 

 much larger than the bacteria and have more striking 

 activities, and rather better development. That is to say, 

 they are more complex. 



These lowly things may be very valuable or very 

 hurtful to man and his interests. The simpler green plants 

 may make and store foods, which in turn may be 

 devoured to support more complex organisms. The bacteria 

 and one-celled animals attack dead matter, and by 

 hastening decomposition serve as scavengers. In this 

 way they destroy dead matter and return the elements 

 that compose it back to the earth and air where they may 

 again enter other plants and animals. But for their 

 action, the bodies of the great mass of animals and plants 

 that die every year would remain to vex us for a long 

 time. Within the moist soil itself they are at work 

 tearing dov/n substances, and thus they prepare the 

 way for other life. Bacteria also help to ripen butter and 

 cheese, to make vinegar, to prepare sponges, skins 

 (leather), flax, and some other fabric plants for their 

 commercial uses. 



The bacteria also do a good deal of damage to man 

 when they attack foods and other materials that he does 



