192 GENERAL BIOLOGY 



holism which is so fundamental in living things should be essentially 

 different in bacteria; it probably is not, and so the usual steps in assimi- 

 lation and dissimilation may be assumed to take place in bacteria. Dur- 

 ing this process enzymes are utilized and toxins produced." 



Bacteria increase with marvelous rapidity by becoming larger in 

 size, followed by a division of each organism into two. If each of these 

 divide every half hour, in twenty-four hours a single bacterium will have 

 become something like 17,000,000 individuals. It can be seen quite 

 readily that such a tremendous increase in so short a time means that 

 vast quantities of food must be at the bacteria's disposal, or the organ- 

 isms themselves must die. If they are then in the body of an animal, 

 the effects of the poisons produced by their dead bodies may be an im- 

 portant factor in injuring the host. 



However, comparatively few types of 

 bacteria are pathogenic. Most of them 

 have some useful function. They are the 

 chief agency . in decomposition and decay 

 by which they help to restore organic ma- 

 terials into the general circulation of na- 

 ture's economy. 



Bacteria spoil food and rot substances 

 which then become soil fertilizers ; they 

 sour milk and ripen cheese; they break 



Fi *' 90 RoX^ d M ( cS. n the down tissues in disease, and aid in diges- 

 i, section of ascending branches; t ion. They, therefore, do much that makes 



6, enlarged base of stem ; *, root- ... 



tubercles containing bacteria. life in the higher organisms possible, while 



at the same time doing many things which cut that life short. 



While it was only after microscopes were invented that bacteriology 

 could become a science, still it has always been known that acid solu- 

 tions and salt solutions keep food from spoiling and that heavy sugar 

 solutions do the same. Thus it was possible to pickle and preserve foods 

 and to make jellies. 



Bacteria require heat and moisture for their growth, so that fruit 

 and meats can be dried, and by preventing one of the important factors 

 for bacterial life from being available, such meat can be preserved for 

 great periods. 



Drugs and chemicals which prevent the growth of bacteria are 

 known as antiseptics. Thus, wine was used as an antiseptic by the an- 

 cients which they poured on wounds. We use alcohol to-day instead 

 of wine. 



In agriculture there are certain soil-bacteria which produce tiny 



