BACTERIA. 17 



has come from the reproduction of one parent a 

 bacterium. Fig. 6. 



Under the microscope these bacteria show three 

 principal shapes. Fig. 7. One like a short, round 

 stick or rod, is called a bacillus and bacilli for the 

 plural. Fig. /b. Another is ball-shaped, called coccus 

 or cocci for the plufal (the third c sounding like s). 

 Fig. 73. A third form which resembles one turn or 

 more of a screw is called a spirillum 

 or spirilla for the plural. Fig. 70. 



These typical forms may shade 

 into each other. The bacilli may be 

 long or short, with pointed/ blunt, 

 or square cut ends. They may be so 

 short and plump as to closely .re- 

 semble a coccus. Fig. 8. The spi- 

 ral forms may curve very little or 

 have decided and numerous twists. 



Fig- 9- 



Bacteriologists do not always agree 

 as to which class a newly found indi- 

 vidual should belong, and to the housewife it makes 

 no difference. 



The bacteria are so simple in structure and so dim"- structure 



Bacteria 



cult to study that there is little to describe. Each 

 consists of a single cell, so far as is known. This 

 seems to have a denser portion on the outside, which 

 forms a cell wall and may be cellulose as in the higher 

 plants. 



This simple cell of protoplasm or "foundation stuff" 



