CHAPTER XXVIII 

 MICROORGANISMS AND SANITATION 



Microorganisms are the lowest forms of life. They are 

 invisible to the naked eye. They are often called germs or 

 microbes, and some of them are of the utmost importance 

 because of their relation to human welfare. 



The plant microorganisms which especially concern us 

 are known as bacteria. Animal microorganisms are known 

 as Protozoa. 



Bacilli (rod-like), cocci (ball-like), and spirilla (spiral) 

 are all forms of bacteria. They multiply in number very 

 rapidly. In a few hours certain kinds increase from a few 

 individuals to 200,000,000,000. This enormous rate of in- 

 crease makes them very powerful organisms in effect though 

 very small and weak individually. They may be foimd 

 almost anywhere. They abound in stale milk, in impure 

 water, and in decaying substances, in which they are indeed 

 the actual cause of decay. 



Certain kinds of bacteria may be easily observed. Set 

 aside a glass of milk for a few days until it sours. Then 

 put a drop of the milk upon a glass slide under a cover glass 

 and look at it under the microscope. The little swarming 

 bodies, each consisting of a single cell, or speck of proto- 

 plasm, are bacteria. The souring of the milk is caused by 

 the action of the bacteria upon the sugar of the milk. Another 

 species may be observed by putting some dry grass in a dish 

 of water and leaving it for a few days. A scum forms on the 

 surface. Examine a bit of this scum under the microscope. 

 The myriads of tiny rod-like structures swarming about, 



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