CHAPTER XXXV 

 BACTERIA, HELPFUL AND OTHERWISE 



Gulliver in his imaginary travels in Lilliput never be- 

 held such tiny plants as actually exist in countless numbers 

 all about us. Many of them are so small that a single plant 

 is not visible to us unless our sight is aided by the most 

 powerful microscope. 



These vegetable growths, or bacteria, are everywhere. 

 They lodge and grow in the cavities of our bodies. They 

 are found in the soil. Thousands may inhabit a drop of 

 water. They even float in the air and are drawn into our 

 lungs with every breath. 



Like larger plant life, some of these miniature growths 

 are very helpful to us in preparing certain foods and in 

 increasing the fertility of the soil. Others are highly dan- 

 gerous, making food unfit to eat or, if they get a foothold 

 in our bodies, causing dangerous diseases. 



Scientists have rendered us a wonderful service through 

 their studies of these tiny plants. Now many facts are 

 known about bacteria that enable us to use some of them 

 for our good and to protect ourselves better against the 

 dangers of the others. It is highly important that we have 

 some knowledge of how bacteria affect our daily lives. 



Bacteria are minute plants, the smallest living things of which 

 we have knowledge. A single plant is less than one ten-thousandth 

 of an inch in diameter. Examined with the highest power of the 

 microscope, each plant is seen to consist of a bit of protoplasm 

 surrounded by a cell wall and, in most species, without a definite 

 nucleus. Many kinds can move from place to place by means of 

 hair-like organs extending from or through the cell wall. The 

 rate of movement is often very rapid. 



Types of Bacteria. There are three general types of bac- 

 teria, classified according to form : spherical, rod-shaped and spiral. 

 The simplest form is the spherical, which sometimes multiplies in 

 such a way as to produce long chains. Rod-shaped bacteria are so 



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