LIFE PROCESSES 345 



higher plants. In changing dea<l matter — plants. Leaves, 

 and animals — to a form which again becomes a part of 

 the earth, bacteria perform a service valuable to man. 

 Reproduction occurs in bacteria through simple fission. 



Sometimes bacteria, break entirely apart, while in other 

 cases they remain connected, forming a chain. Under 

 favorable conditions each cell can grow t « > full size in half 

 an hour and be ready to divide again. It is this abilil 

 to multiply rapidly which makes them of so great impor- 

 tance, for a few hundred bacteria, even of the harmful 

 ones, could produce little effect. 



In the process of growth, bacteria produce two sub- 

 stances, enzyme (see page 172) and toxin (toxin: Greek, 

 toxicum, poison). Enzymes produce fermentation, a break- 

 ing-up process of which man makes use to secure certain 

 flavors and odors, as well as to soften hard materials. 

 Toxins are usually poisonous to living organisms, includ- 

 ing the bacteria which produce them. 



Enzymes cause the pleasant flavor of such articles of 

 food as cheese and butter. The quality of tobacco depends 

 largely upon the kinds of bacteria which have been at 

 work upon it. Such bacteria are classed as helpful, as are 

 those which gather nitrogen for the plants of the bean 

 family. Other helpful bacteria are those which make it 

 possible for man to use sponges by ridding them of t lu- 

 soft, slimy substance with which they are filled when 

 alive, as well as the bacteria which soften the useless parts 

 of the flax plant so that the rest of it may be separated 

 and made into linen. 



When food, air, warmth, or moisture is not sufficient, 

 bacteria cease to grow and go into a resting state. That 

 is, they change their form, and surround themselves with 

 a substance which protects the soft protoplasm from being 

 harmed by freezing, heating, or drying. The simple 



