Intermediate Organisms 



193 



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

 assimilation and dissemilation may be assumed to take place in bacteria. 

 During 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, a single bacterium will have become something 

 like 17,000,000 individuals in twenty-four hours. 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 



important 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 

 materials into the general circulation of 

 nature's economy. 



Bacteria spoil food and rot substances 

 which then become soil fertilizers; they 

 sour milk and ripen cheese; they break 

 down tissues in disease, and aid in diges- 

 tion. They do much that makes 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 solutions 

 and salt solutions keep food from spoiling and that heavy sugar solu- 

 tions 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. 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, the ancients poured wine on wounds as an 

 antiseptic. We use alcohol to-day instead of wine. 



In agriculture there are certain soil-bacteria which produce tiny- 

 galls ( ), commonly known as tubercles (Fig. 90), 

 on the roots of clover and other leguminous ( ) 

 plants. These serve a very important purpose in that they derive nitro- 

 gen directly from the air and supply it to the clover. This makes it 

 possible for clover to grow in soil very poor in nitrogen, while the over- 



90. Tubercles (Galls) on the 

 Roots of Red Clover. 



1, section of ascending branches; 

 b, enlarged base of stem; t, root- 

 tubercles containing bacteria. 



