SAPROPHYTES 401 



of the earth they are present in great abundance. Bacteria 

 are ever present in the soil, water, and air, in the food and, con- 

 sequently, in the mouths and alimentary tracts of animals, 

 and in all decaying organic substances everywhere. 



They are never growing and active, however, unless they 

 are supplied with an abundance of water, a suitable food 

 supply, and a favorable temperature. In the ordinary form, 

 they can endure drouth and remain alive for some time; 

 the different kinds vary greatly in this power, however. Some 

 kinds have the power of forming SPORES which endure drying 

 for many months, some even for many years, and still retain 

 the power of growing whenever they fall into suitable condi- 

 tions. In the formation of these spores, the whole living 

 part of a bacterium contracts into a spherical body within the 

 original cell wall, a new and thicker wall is secreted about 

 this body, the original wall bursts and the spore is set free. 

 The spore is thus a means of living over an unfavorable season, 

 or of resting until suitable conditions for growth return. The 

 fact that bacteria are able to endure drought either in the 

 spore form or in the ordinary form, accounts for their wide 

 distribution and for the fact that they are present and ready 

 to begin active growth whenever and wherever any suitable 

 material is found for them to grow in. 



SOIL BACTERIA 

 456. Study of Soil Bacteria. 



Exercise 93. Soil Bacteria 



Procure some rich soil from a stable lot or a garden. Fill a glass 

 tumbler half full with the soil and then fill the tumbler to the top 

 with water. Stir the mixture thoroughly and allow it to settle. 

 After the soil has settled, examine a drop of the water under the 

 high power of the microscope for bacteria. Examine a drop of 

 clean well water in the same way and compare the number of bacteria 

 in the two samples of water. 



You will get the idea from this experiment that the soil 

 contains myriads of bacteria. In the water taken from the 



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