SHAPE AND STRUCTURE OF MICROORGANISMS 



The cell is the unit of life. This consists of an outer mem- 

 brane containing within it a semi-solid mass of protoplasm. 

 Higher plants and animals are composed of millions of these cells. 



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 0000000 ^J o^ 



YiG, 4. — ^The normal types of bacteria. 1-6 y cocci; J-xSi bacilli 5 14-163 

 spirilla; j, micrococcus; 2 and 5, diplococci; 4, tetracoccus; 5, sarcina; 

 6; streptococcus (the lower chain includes an arthrospore) j 7 and St 

 bacilli, p, to J 12 and jj, bacilli with various granules, ji, streptobacillus; 

 i4j vibrio, 1S3 spirillum; 16, splrocheta trenema (after Kendall). 



The bacteria are single-celled organisms and in shape have the 

 very simplest conceivable structure. Although there are thou- 

 sands of bacteria having many v^ide variations in properties, yet 

 they all have three general forms — ^rod-shaped, spherical, and 

 spiral. 



Shape of Bacteria. — ^The rod-shaped bacteria are cylindrical 

 organisms which may be compared to an unsharpened lead pencil. 

 Some have rounded ends, others straight, v^hereas still others have 

 the ends hoUov^ed out. The size also varies, some being so short 

 that it is impossible to tell v^^hether they are rods or globular or- 

 ganisms. All rod-shaped organisms are knov^^n as bacilli (singu- 

 lar, bacillus). 



Another type of bacteria is the spherical, vi^hich may be 

 likened to a baseball or at times to an tgg. They are known as 



