BACTERIA 



27 



three dimensions, resulting in the Streptococcus, Micrococcus and 

 Sarcina forms respectively, provided that the cocci remain united 

 after cell division has taken place. Streptococci may be com- 

 pared with strings of beads, Micrococci form tetrads, i.e., squares 

 composed of four spheres, and Sarcinse form bundles of cells. 



IG. 27. Bacterium typhosum, peritrich. 

 (After Migula.) X 1,000. 



FIG. 28. Bacterium vulgar e, peritrich. 

 (After Migula.) X 1,000. 



Gocci which adhere together in pairs are known as Diplococci, 

 d those forming irregular aggregates resembling clusters of 

 grapes are named Staphylococci ; these names, however, have no 

 systematic significance. Cocci which divide in more than one 

 direction do not as a rule stretch before division, but form two 

 hemispheres immediately after division. Many streptococci 



a. 



I 



.; 

 * ' 



FIG. 29. Various Cocci. (After Flugge.} x 1,000. 



behave similarly and resemble chains of spheroidal links, flattened 

 as though compressed along the direction of growth. Other 

 streptococci become distinctly elongated, forming oval or even 

 rod-shaped links ; an example is seen in Streptococcus lactis, the 

 commonest of the lactic acid bacteria. With the exception of a 

 few sarcinae, the cocci have never been found to form spores. 



The rod-shaped bacteria are divided into the genera Bacterium 

 and Bacillus. Originally the term bacillus indicated long rods, 



