28 



BACTERIA AND SOIL FERTILITY 



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are extremely small. Even the largest are not visible to the naked 

 eye. The smallest are beyond the range of our most povi^erfiil 

 microscopes. The Pfeiffer bacillus, the organism which v^^as 

 thought to cause influenza, is one of the smallest organisms 

 knov^n. It is a rod-shaped organism, and if placed end to end 

 £fty thousand of them would be required to reach one 



linear inch. It 



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fifteen thousand ty- 

 phoid bacilli to 

 reach an inch. The 

 organism causing re- 

 lapsing fever is one 

 of the largest 

 known, and of these 

 it would require fif- 

 teen hundred t o 

 reach one inch. We 

 often magnify bac- 

 teria one thousand times, and then they appear as dots under the 

 microscope. If we would magnify man to this extent he would 

 be a giant indeed — six thousand feet tall and fifteen hundred feet 

 wide! In a sample of milk containing a billion bacteria in one 

 cubic centimeter there is less than one-thousandth of its volume 

 bacteria. Or, a little globe of bacteria no larger than a drop of 

 water would consist of fifty billion bacteria. 



Movement. — If one places a handful of hay in a bottle con- 

 taining beef tea and allows it to stand in a warm place for twenty- 

 four hours and then examines a drop of it under the microscope 

 It will be found to be filled with living organisms. One notices 

 that all of the particles within the drop are moving^ — even the 

 small particles of hay. There is a great difference, however, in 

 the way in which they move — some swing back and forth, while 

 others are seen to move swiftly across the field and out of sight. 

 All of the bodies which are thus seen to move rapidly are bacteria 

 which have the power of movement. By appropriate methods it 



IiG. 12.- — Successive steps in the formation of the 

 various groupings of the cocci, i, streptococcus. 

 2, micrococcus, with cells arianged in tetrads. 3, 

 sacrma 4, staphylococcus (after Buchanan) 



